If you have other accounts on your xbox, sign in to them and see if the code is there. When I was playing Halo 4, I signed my brother in to play some grifball with me. When I was in the navigation menu, he had a message from xbox giving him a code. He hasn’t even played Halo 4 before Nov. 20th and he never had a Gold account.
So, yea, go check your other accounts if you have them.
Read extra if you want
P.S: I told a friend that I was gonna give a code away on the forums, but he said that he needed it. I told him that I was only giving it away to people that plays halo a lot. He said that he plays it a lot, so I gave it to him. Do I regret it? Yes, because the only games he is playing is Borderlands and NBA 2K. He’s also SR11 and had the game for 2 weeks.