The final block of hearings in the robodebt royal commission began on Monday, examining the impact on victims of the scheme and what government departments knew about its illegality.
The commission heard from Jennifer Miller, whose son Rhys Cauzzo committed suicide in 2017 after being issued with a debt notice of more than $17,000.
Ms Miller said she first learnt of the debt notice issued to her son in mid-2016, which exacerbated existing mental health conditions.
"Unbeknownst to me, he didn't let me know how much pressure he was starting to feel from the debts and we didn't know anything about robodebt," she told the commission.
"He was very distraught when he made that phone call (about the debts) to me and he said he was feeling suicidal."
Robodebt went from 2015 until 2019, recovering $750 million from 380,000 people using annual tax office data to calculate average earnings.
It was allowed to operate for several years despite concerns it was unlawful.
The commission heard Rhys had posted on Facebook in May 2016 about the robodebt, noting he didn't have pay slips from previous years which could be used to fight the notice.
Ms Miller said while she expected her son to still have a vulnerability indicator on his Centrelink profile, it was later revealed such indicators had lapsed.
After her son's suicide, Ms Miller said she tried to gain information from government department and ministers, including then human services minister Alan Tudge.
She said correspondence she received from Mr Tudge following Rhys's death just contained platitudes.
"There was absolutely no genuine effort of trying to give me any information. As far as I'm concerned they were just false words," she said.
Ms Miller said she was left frustrated at attempts to find out the information and only learnt of ways the debt was calculated through the royal commission.
"When I first was seeing a lot of this information, it certainly broke my heart because I felt like I had let Rhys down, not knowing a lot more than I think I should have," she said.
"He was certainly let down by the system."
Commissioner Catherine Holmes last week wrote to the government requesting a two-month extension of the inquiry.
She said since the last hearing block, which began last month, an extra 100,000 documents had been produced.
"The extension reflects the significant work needed to address the terms of reference and the extraordinary volume of material produced in response," she said.
The commission will later hear from Megan Lees, former chief of staff to then human services minister Marise Payne, and Charles Wann, the chief of staff to Scott Morrison when he was social services minister.
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