i have the same problem my pre-order dlc code was used before i even opened the box.
i spent an hour on the phone with EA tech support and they transfered me half a dozen times until finally they said my code was used by someone in another country and that i must have given my code away and said there's nothing they could do and hung up
so after doing some research i learned gamestop's dlc code generating algorithm was discovered and someone made a key generator to spit out codes,so yeah your code was stolen before you got it
example: http://n7warfaregeardlc.blogspot.ca/ (i don't recommend downloading it,it will probably install a virus)
