Unprofessional services, overbilling and braech of contract

I took a phone contract with MTN last year December where the were supposed to debit same month. On the day they were supposed to debit, it bounced because i had transferred all my money to another account and only left with approximately what they were supposed to bill.

I later went and consulted why i wasn't billed (to avoid double billing the next month). To my surprise I was shocked to be told that my monthly installment was over R800 whereas I signed a R269 contract. MTN Boulders wasn't helpful at all because it seems like all their systems aren't even integrated, I had no choice but to go to Mall of Africa (where i took the contract). That time my services were blocked because non payment.

Today I received an sms that about R1682 will be debited from my account; which is for 2 months, okay. But I just signed a contract and all of a sudden what I signed for changes to so much money? Where do y'all get that?

I will not allow MTN to take more than what we agreed on, rather your debit bounce because as far as I know, what I owe is roughly R500.00 and that's what will be in my account on the next bill date.

The query that was said to have been logged ages ago is still not resolved I'm even opting to cancel the damn contract. Very unprofessional, don't even tell me about internal processes and problems; I just want my bill fixed!!!