Asset Recovery Group This has got to be a scam! Oregon

I just received a call from these people claiming I owe $700 to an organization where I purchased some medical equipment.  I had paid for the equipment 4 years ago, in full, and was sent a bill 3 months later for $80.  I called the equipment company and was told they switched to new billing software and that it was a calculation error but I did owe the money.  Ok, why they didn't call me and have me pay it is beyond me.  They sent me to collections (this "Asset Recovery" group).  I paid the $80 and that's the last I heard from them.

Today I get a call from Asset Recovery stating that I owe $700.  I said they had the wrong person.  The woman was HORRIBLY rude and said "Oh I have the right person" and claimed they have sent me "50 letters" (to an address I moved from 4 years ago) and tried repeatedly to call me.  I said "well then you must have received all 50 letters back - and if you called me today and got a hold of me, why didn't you get a hold of me in the last 4 years?"  She ignored me and asked how I would like to pay for my bill today.  This went on and on and I told her over and over again that I DO NOT OWE this money and I will not pay her one red cent.  She got increasingly more rude and said that I was just trying to skip out on a bill.  I of course said I'm not skipping out on anything, and that I don't owe anything to the company that I purchased the equipment from.  She tried again to get information out of me and I said she was wasting her time.  She said she would report me as "refusing to pay" on my credit report.  I said "knock yourself out - I'll just dispute that too" and hung up. 

I think these people use scare tactics and OLD INFORMATION to create new income on bills that have long since been paid.  CROOKS!!!!!!!!!!!!!!