
What about trying Gamestop Customer Service. Explain the situation. If you are a Rewards member they have a record of all the games you've bought/sold at gamestop. That would include your preorder.
Based on that, they would have to give you the key as it's the way to get the preorder bonuses that Gamestop offered.
Based on that, they would have to give you the key as it's the way to get the preorder bonuses that Gamestop offered.