MTN WANTS ME BLACKLISTED WHILE THEY OWE ME!!!

I took out a data contract with MTN in 2015 for R139. In July 2017, on the debit order date, MTN debited R829. I called the MTN Customer Service center and they told me that there was an upgrade to my package so the debited amount includes a cellplhone. I wrote an affidavit as per their advise because I had not performed an upgraded and was told their ***** department will investigate. I stopped the debit order while waiting for the outcome of the investigation. Months went by with no feedback from MTN. On the 28th September, I sent an email requesting feedback. Again, no response. On the 28th of October I was surprised to received a call from MBD requesting that I pay my MTN account because it has been handed over to them for collection. I immediately called MTN and has since then called them several times to address the issue and have them request MBD to stop harassing me. I called on the 2nd, 13th and 15th November for feedback and everytime, I am told that the issue needs to be escalated to some department or another and should call back for feedback. All I want is for MTN to credit my account with the R829 they debited from my account and this will cancel off the R556 (R139 x4) payments I have not made. Surprisingly, MBD is demanding that I pay R1394 for missing 4 payment with MTN. Ridiculous!!!!