The ANZ bank has refunded about $220 million to customers, including $90 million to people charged the wrong interest rate on their home loans.
Nearly 3000 customers do not know they will share a $1.5 million refund by Christmas while a yet-to-be-determined number will be in line for $13-15 million over a different processing error.
Those refunds are the latest connected to mortgage processing errors such as offset accounts not being linked to home loan accounts.
ANZ has paid at least $130 million in remediation to customers over the last decade over a range of issues, the banking royal commission heard on Wednesday.
That is on top of the refunds for various home loan processing errors that currently sit at $75 million and are expected to reach $90 million, mainly for home loan customers being charged the wrong interest rate.
Senior ANZ executive Sarah Stubbings said delivering the standard of banking and financial services customers expected had led to a level of complexity in its systems and processes, which contributed to the issues.
Counsel assisting the commission Albert Dinelli suggested there had been a "bandaid" rather than proper fix of the issues.
Ms Stubbings said the bank had implemented a number of system fixes and noted it was moving to have one, rather than three, home loan origination systems.
The bank made changes to its Breakfree home loan package and linking offset accounts after refunding $69.3 million in 2014 to 400,000 customers who were charged too much interest.
But further customers did not receive the appropriate interest rate discounts or fee waivers in 2016 and early 2017.
A February 2018 ANZ document noted a project team must identify how to "stop the bleed" on issues connected to offset account linkage errors prior to refunding customers.
Mr Dinelli asked if that indicated the bank did not put as high a priority on refunding customers as it should, but Ms Stubbings disagreed.
"As part of any remediation process you actually have to stop the issue because otherwise it's very hard to remediate customers if you've still got customers that are being impacted by it," she said.
Ms Stubbings said the bank had linked the offset accounts but had not yet refunded the interest benefit customers missed out on.
ANZ's head of home loan products said about 2800 customers were expected to be refunded $1.5 million by Christmas.
Ms Stubbings said the bank had not yet determined the number of accounts affected by another issue where customers did not receive all the offset benefits they were entitled to, but expected to refund about $13-15 million by Christmas.