I won a game I've got it already

Send a support ticket!

ask for a reroll.

Just write at the giveaway that the creator please reroll it because you have it already.

Trying to use a key of a game you already own doesn't make the key invalid, so everyting is fine :)

1. remove link to his profile and giveaway.
2. Reroll won't help - ga-creator chose wrong game for giveaway: he has key from dlh.net for Pirates of Black Cove Gold (topware interactive, removed from steam store), but he made giveaway for Pirates of Black Cove (Nitro Games )
   You can activate Pirates of Black Cove if you own Pirates of Black Cove Gold so ask giveaway creator about correct key. He should give you correct key in 7 days, if he fails - mark as "not recieved" and forget about it ^^

just wait 7 days and mark as not received. keep all that proof in case you need it later.