Terrible accounts handling.

Good day I have been living in an estate (Southgate Ridge estate)managed by IHS Property management. I have been struggling with the accounts department. They once over billed me on my water bill and because the account was running on a debit they had to credit me that money back. After confirming that they have over billed me they said that the money would be credited to the IHS Account and that my next rent payment will be excluding the owing amount. This did not happen, so I cancelled the debit option and opted for deposit. When I spoke to their consultant David, he said I should ignore the extra amount on my my statement and just pay the water bill and rent only. I have since been getting torturing sms's threatening the effect on my credit record. I have complained timeously about this and it has still not being fixed. When I call and query this they tell me that they are working on it and that it is a systems issue they have.I spoke to another accounts lady (Thuli / Thandeka)who promised to send me something in writing that confirmed that I do not owe them but still to this day she has not sent it. I have been complaining for over 4 months now. I have never been a bad payer and if this is affecting my current great credit score then I will have no choice but to fight this legally. I just got one of those revolting sms's a few seconds ago. I NEED THIS TO STOP! IT IS NOT MY PROBLEM THAT YOU HAVE A SYSTEMS ISSUE YOU CANNoT TORTURE ME LIKE THIS.