Long cancelled service but continued debit orders - useless cancellations department

Webafrica have continued to debit my account for a fibre service which was years over the original 24 month contract. The service was a month to month service and when I requested a cancellation I received emails and so on confirming the cancellation and instructing us to drop off the router at their warehouse. I have phoned back many many times to get the debit order stopped and each time someone says they will hand it over to their cancellation department.