What to do when winner doesn`t check recieved ?

If 7 days have passed you can ask for a reroll, if he activated the game but didn't mark as received you can send him/her a message or report!

1) Add them and talk to them through steam chat.
2) Comment in one of their giveaways.
3) Comment under one of their comments.

Ended 3 weeks ago

Check their profile if they are even online nowadays on SG, hopefully they are. Try leaving a message them as TLS said before, if no response in a day or max two, file a ticket for force feedback. Not because they need to be punished, but because you shouldn't have unreceived giveaways because the winners acting weird.

You can check if they have the game in question now in their gamelist on steam (they could activate it on a smurf account tho).

Is there a way I can message them. PM or even in comments.

since they are level 1 GA's they had to of made a giveaway in the past.. if their giveaway(s) are public or accessible by you, you can leave a message for them on old GAs too. that'll leave them another notification in the tray that they may just ignore, or may finally respond to and take action.

if they continue to ignore you, then i'd just contact support for a request of feedback & link the comment you made for proof trying to contact them again.