its been 6 months, go to court, with your witnesses and watch him show up with witnesses too.
its hearsay, i would be extremely surprised if you got anything but a "sorry, have a nice day".
Verbal contracts are allowed, but IIRC isnt he under 18? i know hes not 21, so you better make sure he was even an adult when you sold the car to him.
Plus, i dont see a judge giving you anything without it in writing
