For one whole month a brutal criminal gang held and tortured businessman Marc Schiller. Eventually he signed over millions of dollars to them. His story is now the subject of a movie, but the ordeal was much worse in real life

At no point during the production of Pain & Gain, the new black comedy starring Mark Wahlberg and Dwayne Johnson, did Marc Schiller get a call from its makers. This surprised the Buenos Aires-born businessman as he was the victim in the true-life story of kidnapping, torture, extortion and, ultimately, redemption upon which the film is based.

"Since they decided not to talk to me they got the personalities of all the main characters wrong," says Schiller from his office in Boca Raton, Florida. "I knew all these guys."

Instead, the film has been loosely based on a series of articles that ran in The Miami New Times in 1999, which detailed the crimes of The Sun Gym Gang, a group of recidivist body builders who connected through a love of hard workouts and easy money. The gang conspired to kidnap Schiller, a former business partner of one of the men, force him to sign over his life and then kill him.

Daniel Lugo, played by Wahlberg, was the conniving leader and according to Schiller a "lethal manipulator", while in the film he is nothing more than a vehicle for Wahlberg's now trademark brand of comedic tough guy.

"In reality Lugo was a very difficult person to like. He almost had a neon sign on his forehead that said: 'Don't Trust Me.' He was a conman and that is all he knew," says Schiller. "After my kidnapping, in the warehouse, he would go into wild mood swings, one minute a nice guy and the next a raving lunatic. You never knew which Lugo you were dealing with."

Noel "Adrian" Doorbal, played by Anthony Mackie, was his meek best friend and partner in crime, literally the Robin to Lugo's Batman – codenames that the two assumed during Schiller's captivity and torture. "The real Doorbal was a loud sadist that did not like being pushed around by Lugo," says Schiller. "He liked hurting people and volunteered to kill me twice."

Dwayne Johnson's character is an amalgamation of three other men involved in the crime, including Jorge Delgado, Schiller's former business partner who masterminded the kidnap and extortion scheme.

In the film, they come across like the three stooges practising a bizarre act of steroidal slapstick that spills over into violence. In reality, they became the worst combination of manipulation, muscle and murderous intent.

It was Delgado who owned the warehouse where Schiller was taken after his abduction, and where he was subjected to a catalogue of physical and mental abuse that Quentin Tarantino would have been proud to pen.

"I've ended up calling it Hotel Hell," says Schiller. "They tasered me, they punched me, they pistol-whipped and burned me with a lighter. They played Russian roulette against my temple and performed mock executions. I was blindfolded throughout. In fact, they kept adding duct tape so that in the end I must have had up to two rolls around my eyes and face.

"From week two on, I also had a bag over my head and balls of wax in my ears. It was only taken off twice: once to put a sanitary towel under the tape because my face was bleeding so badly, and in the end when they changed to bubble wrap and tape in preparation for my murder."

The men had no intention of killing him at this stage, not before they had forced Schiller to blindly sign document after document, one of which was granting Jorge Delgado the power of attorney over all his business affairs and bank accounts. The men also presented him with a series of spoken "scripts" that he would be coerced to repeat over the phone to his family and business partners until there was nothing left of his life. The gang held a gun to his head while they listened in on an extension.

Marc Schiller in Boca Raton, Florida, in 2013. Photograph: AP/Suzette Laboy

"They told me that unless I cooperated they would bring my wife to the warehouse and rape her in front of me. They also said they would kidnap my son, who was six, and daughter, who was two, and chain them next to me. So I made them an offer. They could have anything they wanted if they let my wife and children leave the country. I felt with them gone, the kidnappers would lose their leverage on me. I had only one way to survive and that was to try to buy my life by giving them what they wanted. That did not work out too well, as we now know."

"I was then forced to call my attorney and realtor to tell them I'd fallen in love with a young Cuban named Lillian Torres and wanted to cash out," Schiller remembers. Torres was Lugo's ex-wife who was named as the sole beneficiary of Schiller's $2m life insurance policy. "I think she was just another pawn Lugo used in his grand scheme," adds Schiller.

The gang had hoped that the transactions would be concluded in a matter of days but Schiller had accounts all over the world and it took much longer to withdraw the money and deposit it into his Miami bank account.

More than four weeks later, Schiller was still chained to the warehouse wall. He was also being routinely abused. Finally, he was told to validate one final piece of unseen paper with his signature. This transferred more than $1.26m of his money into offshore accounts set up by his captors.

Schiller has since seen much of the documentation that he was forced to sign blindfolded and under duress. "It is unimaginable that it didn't raise any suspicions," he says. "The signature that was supposed to confirm a change of beneficiary in my life insurance policy I wrote, on purpose, vertical to the dotted line."

However, with this final signature Marc Schiller had now become obsolete to the Sun Gym Gang who proceeded to force-feed him alcohol and sleeping pills over a number of days before stuffing him unconscious behind the wheel of his car. Lugo gunned the accelerator pedal towards a concrete post before jumping out at the last minute.

Schiller survived the impact. While comatose, he was doused with petrol and a fire was set in the car. The vehicle also contained a portable propane tank, placed there to finish the job. Miraculously, Schiller gained consciousness before the car exploded. He escaped, only to be run over by a waiting Lugo and Doorbal. Determined to leave no loose ends, they then reversed their car back over his seemingly lifeless body.

The intention of the staged crash was so that the corpse would be discovered quickly and the gang could claim the $2m in life insurance, however they didn't count on Schiller surviving the horrific ordeal. Strangely, what worked in the gang's favour was the outlandish nature of the kidnap and torture plot and the astonishing ineptitude with which its final act was carried out.

"The tale I presented to the Miami police seemed so fantastical to them that it was dismissed out of hand as an 'Academy-award-winning performance and story'," says Schiller. However, a highly experienced private detective called Ed Du Bois with connections in the Miami police force took it seriously. Even so, the police department only started to believe Schiller's story when the gang struck again, using the exact same MO and blundered into another bloodbath – this time killing both their victims, Florida millionaire Frank Giga and his girlfriend Krisztina Furton.

One of the most striking disconnects between film and reality is that the actor Tony Shalhoub is not cast as Schiller. Instead, he plays a character named Viktor Kershaw.

"Viktor Kershaw is a criminal prick who deserves bad things to happen to him," spits Wahlberg's character in one scene. In Pain & Gain, Kershaw is an obnoxious bore who brags about his ill-gotten wealth to the impoverished gang members.

"It's 180 degrees from who I am or have ever been," says Schiller. "I was Mr Responsible, Mr Predictable. Clearly, they want the audience to root for these guys in some way, so they don't lose them early on. To not see them as the animals and sociopaths that they really were."

As if the story couldn't get any stranger, immediately after Schiller's extraordinary testimony against his captors – which presiding judge Alex Ferrer deemed "traumatic" just to listen to – Schiller was arrested and accused of false Medicare billing. He pleaded guilty and received the minimum sentence. Judge Ferrer was a character witness at his sentencing.

However, despite the inherent drama of the tale, verdicts on the film have been mixed since its April release in the US. It is the director Michael Bay's eagerness to stress the "truth" of the story makes Schiller uncomfortable.

"The only thing that really rings true for me is the title. My pain really did result in a lot of people's gain. Especially Hollywood's."

• Pain and Gain – The Untold True Story by Marc Schiller is available now