Hi, you are the winner of this GA, pls mark as received asap

https://www.steamgifts.com/giveaway/HHCAn/heaven-island-life

Unfortunately I am not able to use this key.

This is a message I receive from steam:

"The product code you've entered has already been activated by a different Steam account. This code cannot be used again. Please contact the retailer or online seller where the code was purchased for assistance."

What can we do about it ?