Thumb sucking numbers

Their finance department gives awful customer service. Last year I told them to go back to a recording of my call with an agent, who confirmed that once I have paid the outstanding amount my account will be closed. They never got back to me, then early this year I received a cancellation letter from them. I just paid R600 on the 25th of August because that was the balance I kept receiving notices that it’s still outstanding for the last couple of months, but oh behold, I am now receiving a statement that I owe them R1400. Where is this coming from? I am never using this tracking company ever again