Ok I signed into my iTunes account from another pc, and now on my iPhone it says my debit card security code is incorrect. I'm 100% sure it's right. I switched debit cards and it worked again, but I can't use that debit card it's for something else. I reentered my 1st cards info and once again iTunes says it's wrong. Is this on iTunes part or my bank? If it's my banks fault what do i say to them? The card works fine everywhere else!

With iTunes your login name/User name is attached to whatever debit card U are using. U just might have to change the login name you're using because I don't believe iTunes updates that database.