Where did you buy the game? Was the pack still sealed? If it wasn't and someone used your key, make sure that the label with your key, isn't a sticker - they won't help you if it is. If it is, your only option would be to go back to the store, and swop out the key with another and hope that hasn't been used.
I repeat, if the page with your code has the code on a sticker placed inside it, instead of being printer straight onto the page, EA will not help you. At All.