Won the GW got the duplicate key !

Mark as not received when you can, and maybe try to get in contact with the person to see if they can give you another key for the game. If not, then not received.

Have you tried talking to him?

Eeesh.

Inform the giver in the comment of the giveaway.

do i report the guy ,if yes how ?

no
explain in giveaway comments what happened (with screenshots) and ask about new key or write that u agree with giveaway deletion. After 7 days mark as not recieved (if u didn't get new key).

ok will do ,thx