I've dealt with them in the past. Here's what you do: 1.) Keep any and all correspondence from them IN writing. 2.) Use this correspondence as evidence. Submit it to the Fair Trade Commision and file a complaint. Once youve done that comtact your state aty9rney general and they will file formal complaints on your behalf. 3.) Use your written correspondence to open up a dispute to prove the debt us fraudulent. You can do this through credit karma for free. 4.) Once you get a decision from credit karma keep a copy of it so if it pops up again it can be resolved.

They hounded me for years for a debt that I wasn't even legally obligated to pay (I was a minor when said debt occured it was my parents responsibility) that's the pr9cess I followed amd they never bothered me again.
Good luck!