Something similar happened to us as well. Grandma sold her car 15 years ago but did not get a bill of sale and car was never transferred to the new owner on paper. The other guy assured her it was a waste of time and that he’d make sure taxes are paid for the vehicle every year. So for the past 15 years she ends up paying the vehicle tax herself. We were lucky that the guys in the DMV were nice enough to fix this as the car was so old that it’s unlikely anyone is driving it.