I have spent literally hours on chat with XBox support attempting to get my missing Fallout 3 code. I ordered Fallout 4 on July 2nd, and at Microsoft's request cancelled and reordered it twice when no code was forthcoming.
I've worked with 3 separate support contacts, "Roi," "Lailani" and "Toffee" and none were able to resolve the issue. At this point I'm quite frustrated. I was actually told to come here by XBox Support on my last chat session.