See the other messages for who these people are and how they behave. If you want to stop it, send the following letter, registered if possible:
Dear Debt Collector /Debt Collector Attorney:
This will serve as your legal notice under provisions of federal law, the Fair Debt Collection Practices Act (FDCPA), to cease all communication with me and my family in regard to the debt you have previously contacted me for. If you fail to heed this notice, I will file a formal complaint against you with the Federal Trade Commission who is responsible for enforcement, the States Attorney General office and/or the American Collectors Association or local State Bar Association.
I have decided that I do not desire to work with a collection agency under any circumstances. I will contact the original creditor to resolve this matter directly, as circumstances warrant.
You are also notified that should any adverse information be placed against my credit reports as a result of this notice that appropriate legal actions will be taken. Give this very important matter the attention it deserves.
YOUR NAME HERE
National Action Financial Services
168 Lawrence Ball Rd, #105
Buffalo, New York 14211
866-265-5244 x 1058