Kathleen Madgwick told the commission her son Jarrad learned of a $2000 debt in the hours before his death, a few weeks shy of his 23rd birthday in 2019.
Ms Madgwick said Jarrad's mental health was made worse by his dealings with Centrelink when he tried to access income support.
His application for welfare support was rejected after he accidentally provided the wrong document and was instead told he owed money for previous years he had accessed Newstart.
Ms Madgwick recalled her son becoming distressed when he was told about this debt.
He left their home after a frustrating call about his Newstart application. Ms Madgwick later found his body in a nearby park.
Although Jarrad had struggled with mental illness, exacerbated by a period of homelessness and a recent break-up, Ms Madgwick said he was a talented writer who made her proud.
After his death she tried to find out more about his case from Centrelink, a process she said was "excruciating".
But she never gave up seeking information, filing multiple freedom of information requests and writing a letter to former prime minister Scott Morrison and former minister Stuart Robert.
She told the commission she did not receive a reply from either.
Ms Madgwick eventually contacted a journalist about her son's story because "nobody was listening".
"I was searching for reasons as to why my son passed away because I always believed he was meant to be here and he was going to make the world a better place," she said.
"I needed somebody to hear me so that it couldn't happen to somebody else."
Ms Madgwick thanked the royal commission for what she had learned through their work.
She said it would allow her to grieve her son without confusion about the circumstances leading up to his death.
The commission also heard from Taren Preston, who worked as a social worker for the Department of Human Services - now Services Australia - between 2005 and 2019.
After returning from a period of maternity leave, during which time the robodebt program had rolled out, Ms Preston said there was a noticeable change in the culture relating to people who had debts raised against them.
Yet when she raised problems with the way debts were being calculated and gave examples of the distress the system was causing customers, Ms Preston's concerns were dismissed by senior executives.
"We were told it was the way of the future," she said.
"There was a mantra of 'so sad, too bad' that (senior officers) would say when I indicated people were distressed over the matter."
Ms Preston felt a departmental shift towards championing the policy "experts" rather than listening to social workers who advocated on behalf of customers.
Her case load doubled and the number of distressed staff she interacted with also increased.
"I observed customers under the robodebt scheme become increasingly hopeless and they felt as if there was no way out," she told the commission.
Ms Preston said people were becoming lost in the system and didn't understand how the debts were raised.
"To me, it looked like (the system) felt crushing."
The hearing completed a marathon three weeks of evidence from former coalition ministers, senior public servants and the independent watchdog.
A final report will be handed down by the end of June, after the commission was granted an extension to its April deadline.
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