Why won't iTunes let me buy anything?

The account does have money in it. 
When I try to get an app or music from the store it tells me to verify my account and makes me put in my password, then it takes me to edit my payment information. There it says my credit card is going to expire, which I don’t get because I only use iTunes cards. Also, for my payment information it says Visa and then shows the last four digits of what looks like a credit card number but I never used one!