The Central Bank is working with Spanish regulators to end disruption to thousands of credit card holders with the former MBNA, caused by an IT changeover.
Customers have been unable to access their accounts online, change direct debit details, register new cards and are having transactions refused.
Some also say they have not received either a hard copy or a digital account statement for March.
This comes just weeks after the new owners of MBNA, Avant Tarjeta, switched the former MBNA Ireland credit card business to its AvantCard unit.
Customers were notified, via a leaflet posted to them with statements in February, that the account changeover would take place between March 15th and 19th, and that there might be some disruption.
They were told direct debit details could not be changed between January 25th and March 15th. They were also told that online services would be available from last month.
MBNA was one of the biggest credit card issuers in the Irish market, operating from Carrick on Shannon in Co Leitrim.
It was sold by Bank of America last year to US private equity firm Apollo Global Management. It is now being merged with MBNA's Spanish arm, which Apollo also acquired from Bank of America.
The Central Bank says it is aware of the situation.
The National Consumer Agency has also had a number of calls from customers, and is directing them to the consumer banking team at the Central Bank.
Avant Card has not responded to requests for further information from RTÉ News.