Trying to enter my card details and it is saying its incorrect

Hello,

I'm trying to enter my card details in the app store so I can purchase things/download games a couple of days ago this was fine, but all of a sudden its saying my card details are correct and I've entered them numerous times and its still not correct. Ive rang my bank also to make sure my card isn't blocked or anything and everything is fine that end.

Anybody have any ideas or be able to help?

Thanks.