@Nifftymitch Go to this link while signed in to your Stadia account:
https://play.google.com/store/account/orderhistory
Find Tomb Raider, click on the 3 dots, then 'Report a Problem' > 'I no longer want this purchase'. You should get a decision almost instantly (check your email). If you haven't played more than 2 hours, most likely you'll get a refund. If you have, Google is actually making a special exception in this case, so contact support so you can get refunded manually.
Edit: just realized you paid 49 for the game, which means that means you purchased the Shadow of Tomb Raider. This game is NOT part of the exception and you can only get a refund if you played less than 2 hours (and less than 14 days, but it's moot at this point in time)
On various pages they say the free game is Tomb Raider Definitive Edition for 10€/£. Shadow of the Tomb Raider for 50€/£ is not in the December pro lineup. Or did they change the pro game?
@Klonx Only Tomb Raider Definitive Edition is part of Pro game for December. Shadow of The Tomb Raider was never included.