Account incorrectly billed

In July 2015 I was on a premium package, but towards the end of the month I requested a down grade to a compact package. On the 31/07/2015, I called again to check if the down grade will be done, on this day I spoke to Elias who assured me that the down grade will happen automatically. To my surprise the down grade was not done, I called to notify them about this and was told it will happen during the day. The next day after realizing that my package was still on premium, I called.<br> Middle of September my services were suspended and when I called I was told I should pay R1100.00. I told them that I was not going to pay this money because it was their fault. Towards the end of September I called in and spoke to Mpumelelo Kaunda and she promised that she will investigate the matter and get back to me, indeed days later she send me an email apologising for the inconveniency. In the email that she sent, she confirmed that my account was billed incorrectly and that the amount of R677.89 has been reversed and I should only pay R399. My account was disconnected on the 14/07. My attempts of resolving this matter failed, because no one even supervisors are keen to help me.