Fees and charges triggered by mis-sold PPI premiums should be paid back, the Financial Ombudsman Service said after a BBC investigation claimed customers could have possibly been under-compensated by £1 billion.
Principal Ombudsman Caroline Wayman said: "If a fee is the result of the mis-sold PPI it should be given back, and if it's not included that would be a mistake."
She also recommended that credit card customers who fear their fees and charges were left out of compensation calculations approach their banks to discover what happened.
Victims of the payment protection insurance mis-selling scandal could have potentially been under-compensated by an estimated £1 billion, a BBC News investigation has found.
Customers who may possibly have been affected had PPI on credit cards issued by Lloyds Banking Group, Barclays, MBNA and Capital One, the BBC said. All these banks claim to make every effort to pay the correct amount of compensation.
The estimated shortfall uncovered by the BBC arose because some fees and charges that were triggered by mis-sold PPI policies have been left out of compensation calculations, which also involve adding interest, thereby dramatically reducing the amounts some customers would have otherwise received.