I think the lack of replies from the OP speaks volumes. The only place the phone should go is to the police and then it is their problem to find the rightful owner. Thankfully there is a process they follow so it has been known to end well.

But a stolen phone is exactly that. So trying to get your money back from the person who sold it to you is the wrong approach IMHO. The only way to go is to the police. Report the seller. And consider the money you wasted as an investment in your education as you have learnt a valuable lesson from this.