Account billing.

Hi everyone.

Ive had the same apple ID for a few years now. I have regularly made purchases throughout. Yesterday I decided to make a 0.79p in app purchase. It did not work as I didn't have enough money in my account to complete (whoops!). since then I cant even download free apps I have had previously installed and deleted (ie Instagram, fling and snapchat) it asks me to proceed to a screen with my account info and asks me to fill in the security digits field. When I do and click next it says card declined. How can I get round this?