I vaguely remember the first time I paid the licence by credit card, there was some small print which stated that the arrangement would continue until they were informed otherwise - hence the annual charge on the card.
I seem to remember getting a reminder about 2 weeks before the licence expired last September, and it said that if there were any changes to details, I should contact them before the end of the month.
As I've changed my credit card recently, I will have to change the details with An Post next time around. But I expect a reminder!
As an aside, when I closed my CC with AIB, the person went through the direct debits she could see on file. Very useful in case I'd forgotten to switch one of the DDs on the card.