Incorrect billing two consecutive months

Last month this *********** thing of a company debited me R649 and then closed my line. My mom had to go show them the successful debit order and fixed their mess. This month 25July, they debited me R1336, it was an incorrect billing and i incurred as unpaid debit order charge that I will see to it that they pay back. What incompetant people have you hired with billing. Fix this ******* mess MTN!!!!