A Long Island man says he went from being a Merrill Lynch manager to a shattered school janitor after the feds — in a terrible case of mistaken identity — arrested him at work and threatened to ship him off to Mexico to face charges that he had sex with minors.

Philip Simone, a married dad from New Hyde Park, is suing the government in Brooklyn federal court for $2.75 million, claiming his life went to pot after they wrongly busted him for being a child molester.

“They told me they had a warrant for my arrest in Mexico,” Simone, 57, testified at his civil trial Monday.

“I said, ‘You have the wrong guy. I’m just a family guy. ’ ”

Simone said he first learned he was a victim of mistaken identity when federal marshals approached him at his Merrill Lynch desk in May 2008.

They escorted him to a security room, then dropped their bombshell, he said.

“They told me they had a warrant for my arrest in Mexico,” he recalled. “That’s when the room started to spin.

“They told me they were going to put me on a plane right there. I have never been more scared in my life.”

Simone — who worked in the settlement division at Merrill Lynch’s Garden City office for 28 years — had the same name as a man sought by Mexican officials for paying for sex with minors in that country.

An ambassador sent an official request to then-Secretary of State Condoleezza Rice to arrest the wrong Simone — and even supplied his home address and a copy of his driver’s license, the suit states.

After being placed in handcuffs and leg shackles, the bewildered dad — with no arrest history — told agents that he wasn’t the man they were looking for.

Federal prosecutors let Simone out on bail with a warning.

“They told me I had a week to prove my innocence,” he said.

Simone desperately searched for paperwork that could prove he wasn’t in Mexico during the time of the child abuse. His son eventually found evidence online of another Philip Simone in New Jersey — a registered sex offender and the real target of the Mexican probe.

Prosecutors dropped their case four days after his wrongful arrest. He eventually returned to his job at Merrill Lynch after being cleared, but was laid off in 2009 as part of a downsizing.

After going on unemployment, Simone took a school custodian job in Queens.

Simone said he suffers everything from depression to lessened sex drive because of the incident.

But Assistant US Attorney Vincent Lipari, in his opening statement, suggested that Simone was greatly exaggerating his plight to score a payday.

Lipari also stressed that Simone spent a total of only four hours in custody and that his case was dropped in a matter of days.