They threaten people with lawsuits to make them pay. THERE IS NO LAWSUIT. They just claim there is one and hope 1 out of 50 people buy it, and fork over money to "make it go away". They will even go as far as to call relatives / your work in hopes to embarrass you enough so that you will pay.
The only way to make it stop is to file a harassment report at the police station. The police will call them and tell them to back off. I did it, and it worked. The ONLY problem is --- they then sell your info to another company and 6 months later another scam debt collection company tries the same thing all over again.
I've been getting these calls with the same threat for 3 years over some payday loan I supposedly took out 10 years ago. Yes...10 years ago. Thankfully, the calls last a week until I can file a police report, then they go silent for 6-9 months