I agree with the previous rebuttal. You are being scammed to some degree. The best recourse, right now, is to send a cease and desist letter.
The next time they call, after they get through their spiel about being a debt collection agency etc., ask for the address where they would like cease and desist letters sent.
Here is the template I use for such letters:
Per Section 805(C) (15 USC 1692c(C)) of the Fair Debt Collection Practices Act, and except as otherwise permitted by said Act, you are hereby ordered to CEASE AND DESIST any and all further communications with the below named consumer. This order shall apply to all communications including by mail, telephone, or otherwise, and shall encompass communications to any third parties including, but not limited to, employers, relatives, and neighbors.
Any and all violations of this order shall be prosecuted as permitted by the FDCPA, as well as any and all external state or federal laws.
Thank you in advance for your cooperation.
CONSUMER IDENTIFICATION:
[Insert personal information here, but DO NOT give out your full SSN, do it in the format of XXX-XX-1234]
Some suggest sending this letter by certified mail. This is not necessary, but it probably is a good idea.
Best of luck!