I can't get my iTunes card to redeem

If you are getting an error message then what does it say ?

If this page doesn't help, and if it's something that only iTunes Support can help with (these are user-to-user forums), then you can contact them via this page (you will probably need to give them images of the front and back of the card, and possibly its 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