I wonder if it would be a good strategy to call his office, inform them that this bill is well beyond the statute of limitations, and if they continue to pester you, you’ll file harassment charges. I would expect that to dry up this conversation in a hurry. Attorneys enjoy using the law to flog others but they are quite sensitive to being flogged by it when the tables are turned. And he’s clearly out of line. Use that tool; it’s there for that purpose.