ok if you tried using your credit card number and have not been credited with it yet, I would recommend checking your bank statement to make sure Apple didn't take your money and accidentally not credit to your account.
Somewhere in the music store there should be a place to edit your user account, this includes teh credit card number. What you can do is enter the number, purchase how ever much music you can get with that, then take out the number.
Personally I just get gift cards and activate them... It's easier.