Telkom ADSL overcharge

I cancelled my ADSL line in March 2018. Telkom promptly discontinued my service but continued charging me for this service I did not have up until September 2018. I have managed to get some credits from them after scores of phone calls. They still owe me credits for 2 months, +\- R850-00. I lodged a dispute No: ********** 1 on the 07/09/2018 which was acknowledged by SMS. Since then after more than 4 months nothing has happened, I have made dozens of phone calls and spent hours on the phone. I have spoken to several "managers" . Every one promises to escalate this query but nothing more ever happens!