Account Incorrectly Charged

I enquired about my limit with MTN being exceeded when I did not increase my limit and was advised that I should wait for my invoice on the 11th of September so that I can be able to be assisted. The 11/09/2019 came and there was no invoice then I receive my invoice on the 22/09/2019 amounting to R756 when I pay R455 on my account. I called MTN immediately and advised I wont be paying that amount and I get a debit order on my account with R756 that I don't even have nor budgeted that amount 1. I did not increase any limit 2. Did not ask MTN for any free airtime3. I cannot pay for a service that I did not request And I did say the debit order must be cancelled to the consultant but nothing was done. Please sort this matter out and please note I will not be paying for a service I never asked for. Did I call and request any increase from you at any point? No. And who sends a statement 3 days before your payment date. The service is simply ridiculous