Game code redeemed

Hi,
I recently bought a new Xbox One from Microsoft and it was supplied with a digital code for HALO: The Master Chief Collection.

When I put in the code it said it had already been redeemed. I have spoken to Xbox support and Microsoft and they have told me that it has been redeemed but not on my account and cannot tell me who has redeemed it. In the meantime I cannot play the game.

Can you help?