United Processing Group review: Collections 1

THIS CHARGE WAS A SCAM I received a threatening phone call from United Processing Group I don't remember what city they said. They said they have a court case filed with my county's DA office about a payday loan I had almost 4 years ago for around $400. They would not let me off the phone until I paid either the whole balance or a downpayment of 50.00 They said someone was waiting down the street to serve me court papers if I didn't pay and the Sheriff's department will be coming to my home or work to either arrest me. They would not take my cashapp card they said it wouldn't work which I find weird also. which is the only place I had money. I had my boyfriend send me $50.00 to paypal so I could pay them, Has anyone been arrested for this scenario? What should I do? I am now very worried. They said I would have 6 weeks to pay the rest, they have sense not even contacted me about how to pay the balance or anything. i don't even know If I really owe money.