An aged pensioner who feared "losing everything" over an incorrect bill from the Robodebt scheme was forced to make repayments on the debt while she was still contesting it.

Rosemary Gay wiped away tears while telling the royal commission into the Robodebt scheme about her "sheer terror" after receiving a debt notice for almost $65,000.

Ms Gay said the trauma would "remain with her forever".

She told the commission she was living alone, working two days a week and receiving an aged pension when she received a Robodebt bill for $64,998.17 in late September 2016 — due to be repaid in a month.

She said the amount was "impossible" for her to owe: firstly because she had always reported her income "meticulously" to Centrelink; and secondly because she "never earned that much money".

"They couldn’t possibly have overpaid me that amount of money, they would’ve had to have paid me a hugely larger sum," she told the commission.

While fighting back tears, she said her first thoughts were of being forced to "sell her house" and "losing everything".

"Everything I had worked for in my 70 years, I just saw it all going away instantly," she said.

Ms Gay told the commission of the hours she spent on the phone trying to navigate a confusing system to contest the debt.

Staff consultant called 'God'

She said she spoke to numerous Centrelink staff and retold her story countless times, before she was transferred to an official the staff bizarrely referred to as 'God'.

"He said they've put in a new system that hasn't been tested and it has a glitch," Ms Gay said.

He explained that glitch had noticed she made a "larger wage for a week and then multiplied it by every year".

"They therefore considered that I'd earned that figure every week from 2010 to 2016. And it also included interest," Ms Gay said.

"I felt that they were going to work on it and that surely they would see that there isn't any way I owe them any money, let alone any money to that degree," Ms Gay said.

Ms Gay contested the debt and said she felt confident it would be waived.

However, she told the commission she was still required to sacrifice part of her pension as debt repayment, even while her case was being assessed.

"It had a significant effect on me because my earnings were very little, my expenses in living in a home as we all have and my budget would be budgeted out every fortnight," she said.

"Having anything deducted from my pension did place me under financial strain."

'Hours and hours on the phone'

Her debt was reassessed from $65,000 to $6,683.16 in October 2016 – which Ms Gay said she still believed was wrong.

"Again, I was in shock," she said.

"It was hard at the time to control my emotions and discuss it with them because it was a matter of hours and hours on the phone attempting to discuss the situation.

She applied again for a reassessment and her debt was lowered to just $120, in November 2016.

"I was shocked and angry by this time to think that they could initially cause such a traumatic experience to anybody accessing support from a pension," she said.

"That they could turn someone’s life upside down and tell them they had owed that amount of money and then do reassessment and still get it wrong.

"It’s just laughable."