Problem solved.
The problem was that i was sold a fraudulently purchased CS:GO copy through Dispenser.TF for the normal average price (4 Keys) from a trustworthy user.
I was unable to tell Steam to reverse the trade since after the trade i gifted the game through email to a friend.
Finally the trader recognised it was his error so he had just given me the 4 TF2 keys back.
Please, to all the users using dispenser.TF , put your games in sale if you know their origin. If a deal is too god, it may be suspicious.