Cut off - again

MTN cannot process my debit order. Every 3 months or so, my payment doesn't go through. So I pay manually and send through the proof of payment to the email as per the website and their call centre. Sometimes I even get an automated acknowledgement. Then I get cut off. On average, I spend at least 20 minutes a phone call trying to get through to the call centre. More often than not, I am cut off. Currently, you cannot choose to speak to an agent - selecting simply drops the call. ENOUGH. I have asked time and again for a reconciliation of my account since balances change from month to month. I have asked them to move the debit order to another account. I pay manually EVERY TIME I get the reminder. But still my service is cut off. And when I try to rectify it with the call centre I cannot get through - it takes two or three days of persistence before something is resolved. Please tell me what it will take to get out of my contract and move my number to another supplier. I have tried Customer Care emails to no avail. This is my last resort.