A won a game twice

Explain this to the support.

Try commenting on the second giveaway, maybe the creator will read it (though if it's a developer giveaway, I'm not sure about this)... otherwise I don't know. Wait 7 days, mark it not received, then at least you can say you done everything possible... hard to get in contact with developers as they usually just make a giveaway but then don't really take part of the site's life, doesn't really check notifications (endless number of ty, I guess)

Just try to contact him. Leave a message on the giveaway telling him to add you on Steam, add him on Steam, and/or leave a message on his Steam profile if you can. Just don't touch the received/not received button at all. There is no need to fill it in if he will end up rerolling you if you get a hold of him. But, if after 7 days you still cannot reach him, you can then mark it as not received.

Not a new situation.

If you already did what you could to contact the GA creator to no avail, mark as not received, and forget about it.

That guy has dumped more than 25,000 keys on this site and has commented a whopping 5 times. I wouldn't expect to ever hear from him. Best let support take care of it.

I have added him on steam and he didn't answer me. I have explained this to support, but them didn't answer me too, only answered the first contact, the second one no.

Giveaway ended 1 week ago.

mark as not received and don't use the key provided, just that for now till he replies.

Unfortunately, this happens quite often with those giveaways.

You should leave the feedback pending, if possible and attempt to contact the creator. It might take a while for them to respond but that's all you can do for now.

Also, do not use the second key, since if they request a reroll in the future, there will be issues.

Closing but if you have more questions, please contact support.