Gift card is not working well

What is the full text of the error message that you are getting ?

If it's that the card isn't activated, and you've tried going back to the store that you bought it from and asked them to activate it properly, then try contacting iTunes Support (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