I'm in the same boat. Did you ever figure this out?
Here's what I did:
Complained to Google Express about it, saved the chat logs. Saved a copy of
the website promotion. Saved proof of purchase. I contacted Ubisoft and
filed a complaint about the code with proof. Google Express said they
reached out to BestBuy too Few days later I called corporate and went to
the digital download and promotion department. One lady said to contact AMD
(lie) Called back and had a guy review all the open cases and the guy said
he'd send me a code.
Not sure if this helps. Pretty much complain and don't take no for an
answer, provide as much proof as possible
Thanks, I'll give it a shot!