Unauthorized Debit Order from MTN - Horrific Service and Experience

I want to share the horrific experience I am currently having with MTN. I few years ago I took out a wifi contract with 100 gigs data. Approximately 3 years ago their Online Sales Department contacted me offering me an additional 50 gigs to top up my current contract. I was happy with the offer as my price was only being increased by another R100 of so. I was not informed that this 50 gigs was another contract on it's on. Bear in mind by this time my other contract was already expired and I was on month to month which suited me fine. Up until last month I was only paying R389. Yesterday I was debitted R2119 from my account. According to MTN the 50 additional gigs was a contract and expired on the 11 Nov this year. And because I apparently didn't cancel or upgrade before that date. It's now on month to month and I have been billed an out of contract rate. They sold me a lie as nowhere in the conversation was I told this was another contract. I wasn't informed that this is the new amount I will be paying should I not upgrade or cancel. And to top it all off I never approved any debit order mandate for this amount yet that the debit order still went off my account. When I tried to reverse this payment I was told that MTN blocked the debit order so that I cannot reverse it. This is *****ing. They knew perfectly well what they were doing when they blocked that debit order. MTN is HUGE in the telecommunications industry yet they are *****ing from their unsuspecting loyal customers. I managed to speak to someone from their retentions department yesterday and informed her that I am cancelling my contract completely with them. The agent informed me I dont need to cancel my contract. She will put me on another promo package of 150 gigs for R299. And I wont have to pay the R2119 going forward. My question is if it was that simple to put me on something cheaper just because you were losing a customer. Why the hell could I not be contacted regarding the increase in price before my account was debitted ??? I didn't even receive a statement showing the new amount. I didn't receive any communication regarding the month to month amount. I was left all in the dark about this. This amount that was debitted was payment for other debit orders. So now not only have I lost R2119 , I have bounced debit orders and bank charges on top of it all. This is real unfair and unethetical of MTN. They have caused me a great deal of stress and a huge loss of money on my side which btw I do not have. What they have done is sell a lie to make a sale and then ***** from the customer. I want this money reversed back into my account with immediate effect but nobody at MTN seems to give a damn.