Debit card stop working

What does 'stop working' mean, what now happens with it ?

Depending upon what is actually happening it might be because it's a debit card, not all seem to still be accepted by iTunes.

For a card to have a chance of being accepted it needs to be registered to the same name and address (including format and spacing etc) that you have on your iTunes account, and have been issued by a bank in the country where you are (and therefore the country which is on your iTunes account).