Pursuant to 15 U.S.C 1692c (c), you have the right to send the collection agency a “cease and desist” letter which would bar them from contacting you further. If they persisted, you may have an action against them which, if successful, would entitle you to actual damages, statutory damages (up to $1000), costs and reasonable attorey fees. Also, assuming you are a consumer debtor residing in Massachusetts, you may also have a cause of action against the collection agency, pursuant to Massachusetts General Laws, Chapter 93, Section 49.