A Sydney businessman has been accused of ripping off hundreds of foreign students over contracts for 457 and other work visas and making a death threat against a client.

Eddie Kang, the CEO of Singapore Oil, charges students up to $45,000 for providing a job placement and a work visa.

But a Lateline investigation has found that many of his clients get no job, no visa, and no full refund afterwards.

Chhabi Bhusal arrived in Australia from Nepal five years ago. Since then she has gained diplomas in commercial cookery and business.

When she started looking for employers who might sponsor her for permanent or semi-permanent residence she looked on the Gumtree website. There she saw advertisements for Mr Kang’s business.

Singapore Oil’s online advertisements begin: "Dear Potential Clients with Pain and Hardships." But for Ms Bhusal, the pain and hardship was only just beginning.

After she visited Mr Kang's office in North Sydney and signed a $20,000 contract, Ms Bhusal was promised work as a customer services manager at one of his companies, Icon Pacific.

"I was requesting to him if he could show me the workplace where I was supposed to work," Ms Bhusal said. "And he said, 'yeah I can show you tomorrow, I can show you tomorrow'.

"He did that all the time and he didn't show me where the workplace was and finally the visa was refused."

Six months after she signed the contract with Singapore Oil, the Department of Immigration refused her application for a visa on May 24.

The department noted Mr Kang's business had already applied for sponsorship for at least four customer service managers for a small cafe in an Adelaide shopping mall with a turnover of just $250,000 per year.

The following month, Ms Bhusal received an email from Mr Kang that stated: "We hereby confirm that final deadline for 457 visa case for you would be 15th of July 2013. If not approved, the full refund will be made to you."

But that full refund never came. Ms Bhusal got no job, no 457 visa, no full refund.

A year after she signed her contract, Ms Bhusal says she is still waiting on around $7,000.

Victims could number in hundreds: migration agent

Karl Konrad, a former police officer who now runs the migration agency Australian Immigration Law Services, estimates that Mr Kang’s victims could number in the hundreds.

"We suspect there is probably anywhere between two to four hundred victims of Mr Kang," Mr Konrad said.

"It's a bit hard to ascertain at the moment because Immigration won't tell us any precise numbers.

"He's been lodging multiple applications to various government departments around the country and getting multiple refusals."

But Mr Kang rejects the claims made by Mr Konrad.

"It’s not true. Maybe what he meant is in the middle of the process there is a declined case and we always appeal and we make it to the proper stage again."

When asked how many cases he had at this stage, Mr Kang told Lateline: "Around a hundred roughly at the moment, could be fifty."

Claims of death threats denied

Lateline has obtained a recording of a death threat made by Mr Kang against a client of Singapore Oil.

The Nepalese man, who requested anonymity, was planning to take Mr Kang to a consumer affairs tribunal.

During a phone conversation, Mr Kang threatened to kill him.

"I kill you man... Where are you now?" Mr Kang asks the student, "What's your address there?"

When Lateline asked Mr Kang if he made death threats against clients, he said, "No, never."

When Mr Kang was played the recording of the death threat, he denied it was a death threat.

"No, no. I deny that. He did the same thing to me. He said he's going to send me the Nepalese mafia."

Mr Kang's client denies he made a death threat against Mr Kang.

Hairdresser handed over $15,000

Shiva Niraula is another Nepalese national who claims to have been ripped off by Mr Kang.

"In one word he is a conman," Ms Niraula said.

"He cheats you and flies and I'm thinking he will fly from Australia very soon."

A trained hairdresser, Ms Niraula signed a contract with another of Mr Kang's companies, Adelaide Petroleum and Hospitality, in January.

She handed over $15,000 but then found out the company did not have sponsorship approval from the Department of Immigration.

Ms Niraula says Mr Kang still owes her $9000, or $11,000 if you count the interest on the loan she took out to pay the fee.

A foreign student from Bangladesh has told Lateline he paid $15,000 for a visa to work as a cook at another of Mr Kang's businesses in Sydney. When he showed up at the address on his contract, the restaurant no longer existed.

Students' claims are 'vicious rumour'

When asked where all the students' money had gone, Mr Kang responded: "That's another vicious rumour they are spreading at the moment. We don't actually use these people's money for any other investment or something like that - that's not possible."

Mr Kang did confirm he had plans to borrow $7.6 million to develop a site.

When asked if that meant he could afford to pay the students back their money, he responded: "You are principally wrong and that's just an unfounded accusation again - you're trying to say all this money should be immediately refunded to all these people which is not true - they are breaching the contract."

Singapore Oil's contracts last 27 months. Part of the agreement is there should be "no harsh pressure or excessive phone calls or visitation by/from the client."

But the students are frustrated Mr Kang has failed to deliver promised jobs and visas, leaving them owing thousands of dollars to family members and banks.

The students fear they will not get their money back. The contracts state that Singapore Oil is incorporated in Singapore and that the contracts will be governed by Singaporean law.

Immigration officials 'did not want to know'

Karl Konrad says he alerted the Department of Immigration about the activities of Mr Kang six months ago.

"Quite simply it was as if they did not want to know," Mr Konrad said.

"I then put in an email to the manager of the 457 business section in Sydney complaining 'why haven't you contacted me? Why haven't you done anything about Mr Kang?'

"We then got a phone call back saying 'we know about Mr Kang and we're going to do something'."

In a statement to Lateline, Minister for Immigration Scott Morrison said: "My department is aware of the matters raised by Mr Konrad. It would not be appropriate for me to comment on an active investigation."

Ms Niraula still cannot believe Mr Kang is able to hold onto her money.

"In Australia I hadn't seen people cheating each other, because everyone is happy. Everybody is doing their own business.

"This is the first time I have seen the people who are interested to take other's money. You know he's not doing his business. He is ruining our lives for his business."