Got scammed!

I redeemed a random premium steam key. Was already disappointed by the fact that it was some trash game, but then when I actually go to redeem it, it says it's been redeemed on another account and I can't use it? WHO DO YOU THINK YOU ARE?!?!? WHY YOU TRYNA SCAM ME LIKE IM SOME SPED IDIOT? If an actual working steam key isn't there, then don't offer it, simple as that. Greatly disappointed.