For that amount, I would hire a lawyer to investigate exactly what the zoning laws are and see if they are in the wrong. I know there are some towns and counties that their boards think they are monarchs that can just dictate whatever the heck they feel like, so I wouldn't just let them tell you you owe, go read those zoning laws. If they give you any crap about it, go neeked and scare them!
LOL
This is all 20 years in the past, I am sure the statute of limitations is over. BUT I could still go skeeeer them. Of course, I would probably live there for the next 3-12 months.