Wilma Spence, an aged pensioner, received a letter two weeks ago through the MyGov website, informing her of a debt of $61.13, with the period listed on the letter as between July 1995 and 9 July 2019.

Mrs Spence rang Centrelink to be told the money was owed for a period from 1993, when she was newly retired, and was because an "income stream was entered incorrectly," but no other information on how the department arrived at that amount, or whether she was at fault.

Social Services Minister Anne Ruston said on Wednesday "I can confirm that the Department of Human Services have advised me that they made an error and they have apologised for doing so".

Mrs Spence said while the amount was small, it showed a wider problem with the way the department treated people, especially older people who may not be as savvy as her when it comes to asking for a review and using the MyGov system online.

"It's so rude for them to send out a letter and ask for money they say you owe them without getting any facts or details," she said.

Human Services Minister Stuart Robert told Parliament this week that 80 per cent of people told they could have a debt with Centrelink had started paying money back. However, Mrs Spence said it wasn't a sign the program was right, but that people didn't know how to ask for a review.

"A lot pay because they're not aware of what their rights are and whether they actually owe a bill," she said.

"I'm still concerned for the 80 per cent who have paid their debts, how many of those people may not have a legitimate debt?"

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The government has been under pressure over Human Services' online compliance program, labelled "robodebt" by its opponents.

In place since 2016, the program matches Australian Tax Office data with Centrelink income records, averaging people's declared income across the year and raising debts reaching into the thousands of dollars through an automated system with no human oversight.

This week the government has been forced to apologise for chasing the mother of a dead disability pensioner, and eventually confirmed victims of the Townsville floods had also been sent debt notices.

Labor and the Greens have called for the program to be scrapped, with two Senate inquiries set to investigate how the system works and its effects on people who receive the debts.

Naomi Gould, a senior solicitor at Canberra Community Law, says the organisation has seen an increase in people calling their advice line over robodebt issues recently.

"They come in waves," Ms Gould said.

"We usually give advice about appeal rights. Centrelink notices are notoriously difficult to read and have a lot of fine print and these days those notices are delivered by MyGov."

Like Mrs Spence, Ms Gould said people don't know their rights when it came to challenging a debt, and Centrelink didn't make it simple to do so.

"People are not always aware of their right to request a review of a decision if they don't agree the decision is correct.

"If you know what to ask for you'll get a review quite easily, but it's not clear to people those review rights exist."

Ms Gould said the system put the onus on the recipient to prove there wasn't a debt, instead of on Centrelink.

"The starting point is unfair and unbalanced," she said.

Centrelink also had powers to garnish wages, take money from someone's tax return and stop them leaving the country if they had a debt, Ms Gould said.

"It's just a worry that they have power to collect debts when the debt hasn't necessarily been proven."

Canberra Community Law assists people with social security law advice, and their service was "overwhelmed," Ms Gould said.

"There's potentially a far greater number of people that are out there, not getting the advice and that's possibly true particularly in the rural areas surrounding the ACT and other places."