Frustrated by lawyers

Good day I have a bad experience with these attorneys, they send threatening messages they frustrate me. I was handed over to them by an orthopedic. I've been making payments to these doctors and when I had a balance of R1200 they denied my monthly payment of R400 as agreed on monthly basis. They said there was no Ref but when I foned their bank, I was told there is a reference number on that payment. I waited for them to rectify that but they didn't instead they handed me over to lawyers and they want me to pay R7900 which I don't have. I am not willing to pay that amount, it's too much and I can't even afford it. I'm getting ugly messages from the lawyers to pay that amount by tomorrow or sherrif will take my furniture. Please help