Gamestop's policy on faulty codes is very clear and is also provided when you accept the code purchase. In short it says, "If there is anything wrong with the code, it is up to the providing company to fix it." Basically, go back to the microsoft rep and say, "Here is the code that I was issued from Gamestop and their policy says that you guys are the ones who are able to help me. If it is not too much trouble here is the receipt with which I made my purchase would you please be able to issue me another code?" The reason Gamestop is unable to help is because we sold you a microsoft store code and we are not allowed to print out extras by law since it is technically stealing from microsoft. Sorry this wasn't a direct fix to your issue but it is all that you can do at this time. Also, be sure you are entering the code in the right place with all the right letters and numbers. I messed up once and confused a "B" for an "8" and man, was there egg on my face.

Could I just ask gamestop for a refund and ask if they could put that towards $50 Microsft points, incase microsoft doesnt do anything because they really havent done much other than tell me to wait 1-2 days for it to work but its the code itself thats not working because ive gotten my brothers and friends to check and make sure its right but it just says "Code not Found".

Check my conversation with Fire Dragon in this same forum post. Microsoft has noted several codes are faulty and that Gamestop should re-issue you one. I am looking for the documentation currently but if you find it before me I would take it to gamestop and they will issue you a new code with proof of purchase.