Unfair business practice

I received a sms from Colmed saying they were instructed to collect money from me for an unpaid account. I spoke to Marlise at Colmed and told her that the account is not mine. I called the doctor that handed me over. They to confirmed my account was paid up by my medical scheme and had no money outstanding. According to the doctor the account loaded on my name was for a different person. I called Colmed and again explained to Marlise what apparently happened. I asked her to contact the relevant docter to get the facts. Marlise called me back the following day saying she understand someone elses account was loaded on my name but i remain responsible for paying the account and that she will list me on the credit bureau and recover the money me from me as it is my account. I have to send a affidavit and must proof it is not my account even after the doctors cofirmed it was incorrectly loaded on my name.