Tony Barber survived a battle with cancer.

But now the 29-year-old has to battle a bureaucratic nightmare after receiving a Centrelink debt notice for $4500 in the lead-up to Christmas.

His is one of many complaints about the automated Centrelink system the federal government is using to claw back $4 billion in overpayments and the way the system calculates welfare recipients' debts

Mr Barber took time off work in 2010 for chemotherapy treatment and received welfare payments before returning to work in January the following year.

Labor frontbencher Anthony Albanese says it appeared Centrelink had taken Mr Barber's income from the periods when he was working and applied it over the whole year, not taking into account that he was sick, out of action and entitled to welfare.

Mr Albanese said the federal government's callous approach to the problem made him sick to his stomach.

"(Mr Barber) deserves better from our national government than to be treated with such disrespect," Mr Albanese said in Sydney.

"We are saying to the government, put some humanity back into the equation here - acknowledge this has been done in an incompetent and a callous way, and fix this debacle."

But Deputy Prime Minister Barnaby Joyce said he sympathised with people's plights but defended the government's crackdown on welfare overpayments.

"We have to respect the right of the taxpayer... This is the taxpayers' money," he told the ABC.

"I make no apology for making sure that those who didn't need it, who got it, pay the money back," he told the ABC.