MTN - Not cancelling account of deceased for 5 years

I have been struggling since 2019 to close a Mtn account of a deceased person. I emailed the death certificate as requested. The debit order is still going off on our bank account, when the bank returns it Mtn just change the amount slightly and the next month it goes through again. We receive no reply from Mtn only automated replies. This amounts to ***** as the number is no longer in use, and Mtn collects money *****ulently.