Can't Use DLC Cars

I purchased Forza 6 Deluxe for my son for Christmas through Amazon. When I went to redeem the the code through my PC, it auto-logged me into my MSN account and auto-downloaded the game and DLC to my Xbox One account. I was never given an option to choose a different account. Now my son can’t use the the bonus cars, VIP membership, etc. I called Microsoft and they said that there is nothing that they can do (no surprise). I tried uninstalling the game, and reinstalling, but still no luck. How do I get this game transferred from my account to my son’s? Microsoft said that maybe the developer could help, but there is no way to call them. Someone please help. I spent $80 for this game and it will be the last money I spend on this developer if they are unwilling to fix this mess. My son is beside himself and this has ruined his Christmas.

funny how Microsoft always pass the buck
they are the only ones that have the access to change these things,they have access to your profiles …no one else

also not the developers fault that you input the code while logged into the wrong account…can’t blame others for user error …there is an option for logging in and logging out so it is possible to change accounts… xbox support are the only ones that can change things associated to accounts
Maybe ask for a refund from xbox support. .again only ones than can do it