MTN billing me for services I don't have

I've experienced some of the worst service delivery I've ever seen in my life with these guys, I opened up a data contract on black Friday for R499,00 since then mtn has proceeded to bill me 928.99 for the past 6 months or so I then logged in a querry with my local branch in January , only to have my querry attempted to be resolved end of Feb, when I see how the querry was resolved they removed an extra 5g of data that shouldn't have been their and credited me back R317.00 for 3 months, which makes no sense, if you do basic maths 317 is not the diffference between the two amounts, they then proceed to credit me this amount based on the bill that was incorrect in the first place. Which means I still owe money to them R191.00 which was stated in black and white on an e-mail. I then check my statement and realise that they are billing me R750 for the month for no good reason whatsoever...... I ever spoken to mtn directly, I have been in contact with e-hub. I have spoken to 20 different agents, I have spoken to my local branch who can't even explain the matter to me because they are just as confused as I am and I still remains with the same issue, so far I have paid a total of over R5500! For a contract that I should have only paid R 3000 for and still I can't seem to see the end of this. There is no way of even speaking to management or head office for this issue . I am a paying client and have been with Them for 4 year's running, and I need my money back once and for all.