MTN *****ULANTLY DEBITS MY BANK ACCOUNT

I am so disappointed at MTN. I have a contract which l pay cash because of a previous experience. I religiously pay every month on time. I then receive a debit on my bank account. I called MTn for clarity and they said there is no debit made on their system but my bank confirmed the transaction. I reported to mtn as ***** in October and was told they are investigating until now today l have not received any feedback. The bank charges me for reversal of debit order. If this is not ***** l dnt know