Maybe call the local police and explain the situation provide the evidence that the car was sold, including things like the bill of sale, etc.About 6 month ago I give away my old car to one of my friend , I was helping him out . But he seem like so not take any responsibility ( anyway no longer friend) I don’t want go much detail into it .
I sign the title over to his name and drop it at his door . Well few months later I still get the toll bill . I went to Dmv and told them I don’t own the car any more . They say nothing they can do . The owner never come register it but still driving around . They told me get the tag but I have no idea where he now . Lost contact
Then they can pull the new owner over and ticket them for driving an unregistered vehicle.
Or just consult a lawyer that knows about these things, in case things get worse.