Department of Social Services boss Kathryn Campbell says she doesn't accept that people died over the government's robodebt scheme, in a fiery parliamentary hearing on Friday.
The government has begun refunding the unlawfully raised debts, with 145,000 people receiving a cumulative $244 million so far, with hundreds of millions still to be refunded.
Government Services Minister Stuart Robert has said the government expects to pay back $721 million in total.
The Federal Court found last year that the use of averaged tax office data to raise debts against current and former Centrelink recipients instead of using their previously reported fortnightly income was unlawful.
In place since 2015, legal advocates, social services groups and Greens and Labor MPs have argued the program caused immeasurable harm.
Families who believe their loved one's suicides were connected to debts raised against them by the agency have also come forward.
Ms Campbell, who was secretary of the then Department of Human Services when the program was introduced, clashed with Labor senator Deb O'Neill, who read out a letter from Centrelink employees who said they had warned the program was wrong.
Senator O'Neill told Ms Campbell "people have died over robodebt".
Ms Campbell said: "No I do not accept that people have died over robodebt. Senator I do not accept those assertions that are being made."
Ms Campbell said suicide and mental health issues were difficult subjects.
"We have apologised for the hurt and harm but none of us can imagine what goes on in individuals' lives," she said.
Prime Minister Scott Morrison has apologised for hurt and harm caused by the scheme and Ms Campbell echoed that apology earlier in the hearing on Friday, and also apologised to staff members.
Officially known as the online compliance intervention, the then Department of Human Services started a new automated program in 2015 that raised debts against current and former Centrelink recipients if their declared income to the agency didn't match with their annual income data from the tax office.
The exchange came at the end of a terse hearing, in which the committee refused to accept a new public interest immunity claim from Government Services Minister Stuart Robert over legal advice that was given over the program.
The government claims releasing such information would prejudice its case in the class action lawsuit it is defending.
Ms Campbell said she couldn't recall requesting legal advice over the program in 2015 because income averaging using tax office data had been in practice at the department for many years.
Labor and the Greens are calling for a royal commission into the robodebt scheme, but the government has so far rebuffed those calls.
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