False advertising. Misleading information

So I'm told I'm due for an upgrade, I go to the mtn store to choose the phone I want and get everything sorted. I'm given a mtn catalogue where I can choose the type of contract that I want. So I choose a note 9 small plan which clearly showed that it was for R799 a month. At this point in time I'm assured that everything I'm seeing on that catalogue is as it is on my contract. Comes due date for debit orders...they debit R1199 from my bank account which of course declines because that's not the amount I expected to be billed. Nevertheless I try to sort it out,I call the customer service line only to interact with a rude woman who showed no interest in helping me what so ever. I eventually go to the store to now make a payment of R1200. My biggest frustration is no one could explain to me how a contract that was on promotion for R799 suddenly became R1199 none of their consultants helped me understand this. I had to get the invoice first to make some sense of this,never mind tax I understand that but how is it now that I'm paying an entirely different amount excluding tax,if tax is their excuse? and of course by then its already too late because I've signed for everything so now I must pay that R1199 for the next 11 months. I'm disgusted, extremely disappointed and very irritated by this. It wasn't planned for but now I'm obligated to pay for it. Mtn is clearly the worst when it comes to customer service. The only thing they care about is getting your money nothing else. Quit false advertising and actually let people know exactly what to expect. You are no different from ****s.