Poor Customer Treatment

I have been a customer of MTN for many yrs. 3yrs ago I added an internet ****le to my contract .This brought my contract payment pm for both to R360 - R390 per month, paid via debit order without fail. Mtn failed to inform me that the ****le contract had expired and proceeded to bill me at out of bundle rates. 2 months ago I received an sms from MTN to say that I owed them R2800! We tried calling their call centre on numerous times and have countless ref numbers and even went in store, without anyone able to assist us adequately. We've tried to reason with the consultants, asking to cancel the ****le, so we could find a way of sorting out the balance they claim we owe them.They say they can only cancel once the increasing balance is settled! First it was R2800, now its on R6400. We tried contacting their credit/legal department but have been told to send an e-mail which no one responds to. Since the first sms we stopped using the ****le but they continue to increase the balance. How am I supposed to sort this out when the balance keeps increasing. We stopped using the ****le immediately but the balance keeps rising. I am at the end of my tether with MTN.