This sounds like one of those "fell off the back of the truck" sales. If this phone was stolen, careful how you proceed. It's unlikely you'll get your money back. If you purchased through a website, report it to them that you were sold a stolen phone. If you bought it direct from an individual, I would go to the police and turn it in. If you are caught with it, you could be charged with possession of stolen goods (at least in the U.S.). So your best course of action is to be proactive and turn it in. If not to the police, then to the carrier if you can figure that out, or to the manufacturer.