Should I contact support?

Yes you should,that may be considered a scam :/

If you have not patience then contact support(best option)! Or else, wait 7 days and do what UnrealrageSRB told!

what game did you win?

you should wait until the guy add you, IF he don't add you after 7 days of the end of the giveaway THEN you add him, if he ignores you just mark as "not received"
add the creator of the giveaway is unpolite plus you can get blocked and never get the game

Dont contact support. Wait 7 days if not received mark as such.
Nothing more nothing less.