The Commonwealth Bank continued to offer card limit increases to a young man deep in credit card debt after he told them he had a gambling problem.

Key points: David Harris racked up over $35,000 in CBA credit card debt

David Harris racked up over $35,000 in CBA credit card debt He was offered more credit after telling bank about his gambling problem

He was offered more credit after telling bank about his gambling problem Commission told bank failed to properly pass on gambling problem information

The banking royal commission heard evidence from David Harris, who racked up over $35,000 in debt on CBA credit cards.

Mr Harris is one of more than 2,500 people to date to make a public submission to the royal commission.

He told the hearing he had never had a credit card before, but applied for one in late 2014 to fund dental work and a trip back home to England.

He was approved for a $10,000 credit card with the Commonwealth Bank.

Commonwealth Bank customer David Harris testified at the banking royal commission. ( Supplied )

He initially paid it off frequently but in the first half of 2015 he began gambling regularly, transferring cash from the credit card to his CBA transaction account to fund the habit.

"I'd max it out, pay off chunks," said Mr Harris, a roofer who was earning $70,000 per year at the time.

By May 2015, Mr Harris said he was "panicking" about how to pay off the first card, so he got a second CBA credit card with a $7,000 limit.

"The only way I could see out of it was to try and win some money to pay it off," he said.

Later that year in November, Mr Harris was approved for a third, $8,000 credit card.

The cycle continued and Mr Harris was soon offered an increase on his first card, taking his total credit limit to $27,100.

He later consolidated the three cards and told the commission he tried to work six to seven days a week in an effort keep up with the repayments.

In October 2017, Mr Harris phoned CBA to change the address on his account.

During the call he was told he was eligible for another credit limit increase.

He told them about his gambling problem and asked them to stop the offers.

Ten days later he received an offer in the mail to increase his limit to $32,000 and around four weeks on, another offer for a $35,100 limit.

"They can clearly see I've got a gambling problem because of the transactions I've been making, I don't understand why they keep offering me more money," he told the hearing.

Mr Harris said he ignored the offers for more than a month, despite notifications reminding him whenever he logged into internet banking, but eventually gave into temptation.

He said he used the whole amount within one or two months.

"Two of the hardest things you can do with any addiction is, one, admit you've got a problem, and two, reach out for help — and in that phone call with Commonwealth I tried to do both," Mr Harris said.

"I tried to reach out for help and I couldn't get any, I got the opposite, I got credit limit increases sent through and I tried to tell them I had a problem."

'Slippery slope': CBA to flag problem gambling

Mr Harris reached an agreement with the Commonwealth Bank to reduce his debt by $10,000 and stop future interest and fees.

He still owes $23,400.

CBA's executive general manager of retail products Clive van Horen followed Mr Harris in the witness stand and admitted the bank had made a mistake.

"We've acknowledged that we should not have provided that final credit limit offer," Mr van Horen said

"That information [about the gambling problem] was not in any way passed through to credit decisioning systems and that's a failing, and we acknowledge that and we've got to find ways to address that."

Mr van Horen said CBA has since implemented changes that flag customers who are spending large amounts on gambling, in either their credit or debit accounts, and will not offer credit limit increases to them.

However he said measures that go further could put the bank on a "slippery slope".

"The choice we've grappled with is at what point do we say it's not OK for an adult to choose how much to spend on different activities," he said.

"If we say you can't spend on gambling, then what about other addictive spending on shopping or on alcohol?"