Nuvell They gave me an extension and then harassed me and lied and said they didn't...I have the paper work!!! Internet

Two years ago, I became very ill and was hospitalized. I had never been late on a car payment and due to my illness, became two months behind on my loan. After returning home from the hospital and listening to the MANY messages from them I called them back. They told me they had a man "in-route" to pick up my car. Frantic I asked "what can I do." The girl was very nice and told me she could give me an extension on my loan. I took it and believed everything was fine. I received the confirmation papers in the mail and was at ease with the situation...Two weeks later a woman showed up at my home with reposession papers and a tow truck. I was stunned. I showed her the papers and we phoned Nuvell together. She explained that she had the papers granting me the extension. After she got off the phone with them and left, I recveived another phone call...same day. The woman on the line informed me that she was a supervisor and that my extension was not going to be granted because I did not send them the papers they faxed me with my signature... "WHAT" I do not have a fax! How could she have possibly faxed me anything..Liars! She informed me that the state I live in requires a signature and they had a man "in-route" to pick up my car. ok, I have heard this before and nobody showed the first time they said it and I knew nobody was coming that time. I informed her that I would seek an attorney and we would handle it in court. I hung up on her. I have been harrassed since for the money on that extension. I won't pay it. I will ignore their nasty comments on my voicemail but..they have gone to far, Somehow they found my sister-in-law, by marriage., and she is married and has a different last name. I have never used her name for anything other than a baby shower invite. However, they found her and are now harassing her and I on a daily basis.. What can I do? Someone help!!!! I have paperwork that granted me that extension. How can they get away with this?