Credit card firm MBNA has been fined €750,000 by the Central Bank for over-charging almost 400,000 customers interest charges amounting to €17m
The breaches occured between July 1 2007 and October 26 2009 and resulted in 373,105 customers being over-charged a total of €16.9m.
MBNA notified the Central Bank of the error when an internal review found that the method of charging interest rates didn't tally with its terms and conditions.
In error it applied interest on customers charges from the date of the transaction rather than the date of the statement.
It also applied interest charges erroneously to customers who were using their accounts exclusively for cash advances but paid off their balance every month.
The Central Bank said MBNA reported the failure in a timely manner and had re-imbursed customers.
MBNA had failed to 'act with due skill, care and diligence' in the interests of customers, and that it failed to put enough resources, checks and controls into making sure it complied with the consumer code, said the Central Bank which investigated the problem.