I bought an iTunes card and it says that is not fully activated

Are you able to try taking it back to the store that you bought it from and ask them to activate it properly ? If not 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 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