AMP charged more than 4600 dead superannuation customers for life insurance, despite knowing there was no longer a life to insure.
Australia's largest wealth manager owes the deceased super members' estates about $1.3 million in insurance premiums and lost earnings.
AMP knew about a similar issue in 2016 but only started investigating in April, after revelations at the banking royal commission about some Commonwealth Bank of Australia advisers continuing to charge dead clients fees.
In the latest case of a financial services company charging dead customers amid a wider fees-for-no-service scandal, AMP continued deducting insurance premiums despite being told they had died and their death claims being processed.
AMP blamed a number of system errors that meant it either did not stop deducting the premiums or did not process premium refunds owed to them.
It has so far identified 4645 customers with $1.3 million in premium refunds owed, but AMP executive Paul Sainsbury said an investigation was continuing into whether other fees were deducted in error.
"It does appear as though there are other fee types that have been deducted post the date of death that will need to be refunded as well," AMP's group executive wealth solutions and customer told the inquiry on Monday.
The royal commission heard about a similar issue in 2016, when AMP staff questioned whether it was appropriate to continue deducting life insurance premiums even though they would be refunded once the death claim was submitted.
Mr Sainsbury agreed stopping the premiums being charged when AMP was notified a person was dead seemed a rather obvious step.
But he said the system in 2016 was coded to refund it when the claim was admitted.
In one case, premiums continued to come out of a customer's superannuation account in June 2016 despite AMP being told of the death in February 2015.
The issue had caused other complaints about policies being closed due to lack of funds in the super account after premiums were continually taken out, an internal AMP email showed.
Mr Sainsbury said the issue this year, which was reported to regulators in June, was that amounts were not refunded to the member's estate.
"The issue in 2016 was not that they weren't refunded, it was just that they were refunded at a different time and we should have stopped deducting them on notification of death."
Mr Sainsbury agreed with royal commissioner Kenneth Hayne QC that AMP had charged for something it was not entitled to charge.
In a statement, AMP said its policy was to refund insurance premiums from the date a claim was determined back to the customer's date of death, which could take some time because the claims assessment process was complex.
CBA and National Australia Bank have both admitted charging advice fees to dead super customers.
The fees-for-no-service scandal led to the departure of AMP's CEO and chair in April, as barristers for the royal commission suggested the company face criminal charges for lying to the regulator.