not debiting and account is always in arrears

I have been battling since February with MTN they just not debiting from my account, I have to phone 808 every month and ask a consultant to put the debit order in place. I later learnt that my account was in arrears and they assured me that once I pay the amount the account will be up to date which I went to pay and when I got a email with my statement for August an extra R500 was added to my bill, I phoned and asked why they said the account was in arrears even though I paid the amount to settle it in June the account is still in arrears. I am very unhappy with MTN and the services that they've given me. I phone on the 26-08-2015 to put a debit order in place and they still haven't debited from my account.