R40000.00 Debit order? I have no MTN contract

MTN has debited me three times in the last three months for amounts in excess of R30000.00. Despite treying all channels to log and resolve a complaint, you still debit my account. I have no contract or business with you. Every time i need to visit my bank to reverse, the is a nuisance never mind the shock of receiving this sms every month. Why can no one help me or stop this?