HELP!!! I have a problem with my purchased DLC

My Forza Horizon 2 Furious 7 Car Pack and my Day 1 Edition DLC are missing even if I already purchased them.
I switched from an old xbox one to a new one last summer so I think that might be the cause of this. The cars are in my garage but when I click on them to drive them, it tells me that either there was an error or that I have to buy the pack. Can someone help me please?!?!

You need to re-install the DLC files.

  1. Menu botton on the game, under my games
  2. Manage game

You will see the local game data on the left, your DLCs in the middle and your savegame on the right.

Download and install your DLCs. After that you should ‘hard reset’ your XB1.