Unauthorised debit orders by MTN

On the 22nd October I made a payment of R560 to MTN to have my cell phone services unsuspended, emailed my proof of payment through to Ayanda Jack at MTN my sim card would also be later converted to prepaid since my contract was ending as per my request . I should mention that prior to this I had made lengthy calls to MTN because each time I would be sent threatening SMS about my services being suspended unless I pay a certain amount I would pay the amount stipulated but the next month the amount would have doubled, I tried several times to resolve this or get answers from MTN but no one could assist until I referred my query to HELLOPETER and I was told to pay the R560 as that is the amount I owe. I made that payment to MTN and sent the proof of payment to Ayanda Jack and had my sim card unlocked and also received sms 's the same day advising that my sim card will be converted to prepaid. 2 month later, December the 2nd MTN tried debiting my account with R155, I called the call centre asking to be put through to the accounts department to no avail , I then sent Ayanda Jack and email but got no response, why wait for 2 months after I was converted to prepaid to make deductions