Debit order query

I updated my bank details telephonically in October. Since then MTN has continued to debit my old bank account. I have called 6 times since October and every time you confirm that my bank details have been updated. This is INCORRECT!!!

The bank charges me for every unpaid debit order! You are costing me money due to your utter incompetence!

The agent I spoke to this morning was so unfriendly and unhelpful. She imp**** that I **** about the debit order even after I offered to show my bank statement. When I asked to speak to a team lead or manager I was told that someone will call me back. She shouldn't be in the phone!

I've been a client for close to 20 years. Your service is shocking. I'm disgusted.