Adr group Nationwide

*I received a call from someone saying there was a civil lawsuit against me and to call adr group with claim number once i called i was advised it was for a debt from 2010 from an address i never resided at. I asked to be faxed a bill to verify who the bill was for and i never received the fax. So i assumed it wasnt valid. 2 weeks later I got a call again stating to call another number when I spoke with someone she advised me I never called their company and the debt was from 2002 and they had my current address. I asked her to fax me a bill showing exactly what I owed. She did but the fax stated i owed adr for verizon. I called again asking for the actual statement and when i did i was transferred to someone who threatned if i did not pay i was going to be subpoenad . I advised them to please provide me with a bill to see if is valid. I am refusing to pay until it can be proven that this is a valid debt *