Well, it's unfortunate to hear that you are being harassed and also in an unprofessional manner by an attorney who is trying to collect on a resolved debt.
You have a few options, ranging from ignoring the attorney, to sending them a cease and desist letter, all the way up to seeking legal representation to sue the attorney if you think he has violated the Fair Debt Collection Practices Act (FDCPA).
If I were in your shoes, I would probably start by sending him a cease and desist letter and also a debt validation letter. See this informative site for help on free forms that you can complete yourself: http://www.bills.com/debt-DIY/
You can also seek counsel from a local attorney, but hopefully he will disappear, assuming that you did indeed settle the debt in question.
Also, just so you know... I answered a question similar to yours in my blog recently. Please go to the following link to read my answer to a fellow reader: http://www.bills.com/being-harrassed-by-collector/
I hope this information helps you Find. Learn & Save.