I asked them (Valve) if they can remove my key or ban this key. I also mentioned that I don't want this key to be working on steam. This is the reply:
Hello,
"A staff member has replied to your question:
Hello,
Thank you for contacting Steam Support.
We apologize for the delay.
Steam game subscriptions, CD keys, and redeemed gifts are non-transferable and cannot be reset or moved between Steam accounts.
We will be unable to transfer this game to another account. You must be logged in to the original account it was registered to in order to play the game.
Similarly, accounts cannot be merged"
This feels like stupid bot asking the question...