I tones problem

Most of the people on these public forums, including myself, are fellow users - you're not talking to iTunes Support here. I've asked the hosts to remove the gift card code from your post.

Was the iTunes card issued in the same country as your account is based (they are only valid in their country of issue) ? If it was and this page doesn't help then you will need to try contacting iTunes Support (you will probably need to give them images of the front and back of the card, and possibly of the receipt) : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page, then iTunes Cards And Codes