MONEY MAKING COLLECTION AGENT SCHEME

I need to understand what goes on with Ampath. I have collection agents from multiple collection companies calling me for different blood accounts. I have already paid 2 and now i get 2 more phone calls with a bill totaling more than R 600 and I already paid R 500. I dont understand what your collection procedure us and this is becoming extremely frustrating. To add on it, your collection agencies have no call centre/collection agency. Is this a money making scheme as I know that my medical aid would of covered this . Im frustrated and tired of these calls. How does my account go straight into collection when i haven't even received an outstanding bill. Your service is horrible.