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.

Did you perhaps mix up the keys or give one twice? "MEXXX-XXXXX-XXX40" was the one i received, already used.

As in the FAQ, ".....In all other instances you should mark the gift as "Not Received" one week after the giveaway has ended.".