Cancellation of Contract & Reversal of Debit Order

Hi MTN. I wrote a notification to cancel my contract but I'm yet to receive feedback from MTN. I have called 135 several times but I'm kept waiting with no-one picking after I try to get to the Cancellations/Retentions department. My contract ended at the end of June but I was debited an additional R700 this month. I keep getting notifications reminding that I'm due for an upgrade - I'm definitely not interested. My contract number is A*** and the reference number for my cancellation is #***. This is just reminding of the poor experience I had two years ago - one would think a communications company would be easier to get hold of. Please assist.