Unauthorised debits by MTN

I am now at my wits end. MTN has been debiting large unauthorised amounts since November last year. I have sent emails, made a million calls and I keep getting contradictory feedback. One minute they will credit my account the next minute oh no everything seems fine with your profile. They have even debited me outside my debit order date. This has really affected my finances and it seems the query is not getting the attention it deserves.