A Question

You should contact the maker of the giveaway and let him know the key was a duplicate,

why did you contact the guy and talk to him, maybe he sent you the wrong key.....

sounds like a douche move to just not say anything, wait 7 days, and mark it as not received.

why put that kind of stress on another human being?

I did contact him right after it said the key was duplicate and he offered me like 3 other games that are worth like 50 cents and I have no interest in. He said he didn't have another copy of Supreme Commander. He started actually yelling at me for speaking English because he didn't understand it. When I asked what language he spoke so I could use Google translate, he just removed me. I should have mentioned that in the post.

You're doing nothing wrong.
In fact, you shouldn't take a key for any game other than the one you won - otherwise you'd be risking suspension yourself.

I was going to tell you to remove the giveaway name from the op, because we could use it to see who it was that didnt deliver (calling out) b ut that game doesnt show in your won list.... what gives lol.