I think I won a fake giveaway...

So 3 days ago I won a DOTA 2 giveaway, and up until today I heard nothing from the gifter. Today he sent me an email telling me that if I want the game, I need to sign into some Steam account that is different from the account that he is using. Steamguard was of course on so I could not get into the account. I saw that he was online and sent him a message telling me about the problem. He responded and told me to use the username and password he sent me. He never responded when I told him that it is impossible to do so because of Steamguard and that it's against the Steam TOS. I looked in his inventory and saw that his main account does not have an extra DOTA 2, I tried Googling the account he sent me and was not able to find a Steam account with that username that has and extra copy of DOTA 2. He still will not respond to me. I know that I have to wait a week until I can report him, I really hope that I don't have to and he gives me the game, but it's not looking too good right now...