Harassing me for a bill I settled.

In February, I underwent some tests and paid my doctor's bill. While waiting for the results from Ampath, I received a statement requesting payment of R623.90, which I settled and subsequently discarded the bill. However, four months later, I received an email stating that my account had been handed over to debt collectors, despite my knowledge that I had already paid the bill. I sent proof of payment (POP) to the debt collectors, only to be told that I need to pay an additional R415 for SMS fees, email fees, and account arrears fees. I find this completely unacceptable and frustrating.