Matthew Thompson, who lives on a rural property in Tasmania, was incorrectly told he owed $11,000 for accessing Newstart and the sickness allowance between 2012 and 2015.
Mr Thompson worked casually as a photographer for the Hobart Mercury newspaper and had fluctuating shifts and income.
Recently diagnosed with generalised anxiety disorder, Mr Thompson told the commission he had struggled with his mental health throughout his life and at times it impacted his ability to work.
He described feeling "shocked" at receiving two Centrelink letters in 2018 raising the debt and had to find his pay slips from the period, which took a lot of time.
"I've been on and off Centrelink since I was 20. It was easier back then, it was face-to-face and there was more humanity," he told the commission.
"These days I can be on the phone for hours (and) sometimes they hang up on you ... dealing with Centrelink is a full time job."
Mr Thompson later had his Newstart debt reduced and eventually wiped.
In August 2020 he received a letter saying Centrelink no longer calculated debts in the same way and it had been reduced to zero.
"There was a bit of relief but the damage had already been done," Mr Thompson said.
"The way they write 'we no longer do this', wouldn't it be nice if they said 'sorry, we don't do this anymore'."
Mr Thompson followed the royal commission closely and felt compelled to give evidence after he watched former prime minister Scott Morrison being questioned.
"After Scott Morrison's appearance - I was watching the whole thing - that night I couldn't sleep. I was furious and wound up," he said.
"The robodebt scheme has had a lasting effect on me as it had on many others. It made my mental health worse. It made me feel like a criminal and a cheat."
He said the way politicians talked about people who needed support made him feel "sad and sick".
"(Coalition ministers) were the architects of the scheme which caused so much harm ... and they continue to blame others," he said.
"It seems to me that the powerful people are always able to take advantage of vulnerable people and the gap between rich and poor increases.
"No matter how many royal commissions we have it always seems to be the case. I hope this commission changes that."
A former public servant accused of withholding legal advice about the unlawfulness of the scheme will also give evidence for a second time.
Annette Musolino, the former chief counsel for the human services department overseeing the scheme, will be questioned on Wednesday.
Former department secretary Renee Leon, who is now vice-chancellor of Charles Sturt University, told the commission on Tuesday Ms Musolino did not communicate that she was aware of legal advice which questioned the legality of income averaging.
Professor Leon said when media reports about problems with the scheme began to surface in 2018 she asked Ms Musolino if the department was confident the program was lawful.
She told the commission Ms Musolino assured her the department was confident about its legality.
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