More than 77,500 Centrelink robo-debts have been reduced, waived or written off, new figures by the Department of Human Services have found.

The stats cover the period from when Centrelink started its automated debt recovery system, dubbed robo-debt, in July 2016 to December 2018.

During that 18 month period, more than 927,000 initial assessment letters that went out. That's the first letter Centrelink sends out to people saying there's an issue and asking for clarification.

From those 927,000 letters, just under half - or 445,000 - debts were raised. (An individual can have more than one debt raised against them if they've received social security payments on different occasions.)

Of that nearly 445,000, 17 per cent - or nearly 77,500 - were either reduced, waived or written off.

About 15,7000 debts were reduced to zero, and a further 27,300 debts were waived or written off. A debt may be waived or written off if a person is deceased or declares bankruptcy.

Few people undertake formal appeal

The new figures were released in response to questions asked at Senate estimates last month.

Greens Senator Rachel Siewert, who asked the Department for the figures, told Hack that only a fraction of people undertook a formal reassessment process.

"The numbers of people who have gone through the appeals process are relatively low, and I have strong concerns about that," she said.

"This is consistent with the strong anecdotal evidence that I'm getting from people who are saying they're too exhausted by the process and are scared and nervous about challenging further."

Senator Siewert said it isn't easy to get a debt waived by Centrelink.

Many people would not have kept their wage slips from years ago. The whole system is rigged against the person on income support.

Brodie was one of the people who managed to clear his debt entirely.

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He got in touch with Hack via Facebook.

"If you can prove you don't owe it then they [Centrelink] will refund any payments. I made a $80 payment to keep the debt collectors quiet, and was refunded my $80 dollars and my $900 debt was wiped when I finally proved [the debt was wrong]," he wrote.

"It was so unnecessary though since it was my workplace's fault that I was in the situation."

Senator Siewert said the Government should pause the robo-debt system until Centrelink can iron out issues to guarantee that debt notices aren't sent out to people who don't owe anything.

She said people who've been slugged with a debt they think is incorrect should appeal.

"Seek advice, challenge it. Approach community legal services... as to what they do about it. Don't just take it because it's from the Government as being right."

Earlier this year, Hack reported that 2030 have died since receiving a debt notice.