Cant edit my payment information

I went to download/update a new app on my phone and it said "verification required" so I press "continue" it then brings me to my account settings and it says my credit card security card is needed, as well as the expiration date being empty so I put both in according to my credit card and click done. Then it comes up saying "your payment method was declined. Please enter another payment method". Ive tried it a number of times from my phone as well as going straight to iTunes on my computer and nothing will work. So until this is solved I can't download free apps, update my apps, or buy music, tv shows, or new apps.