My game can't Activation key on steam please help.

I just bought this game a few minutes ago but it doesn't work please check me

The product key you have entered has been activated by another Steam account. The key is no longer available. Please contact the retailer or online seller where the code was purchased. to get help

I contacted Support this morning and until now no answer as to why. The key was already used even though I just bought it.

anyone can Help?