Continuing with debit order long after termination of service

we had to close our guesthouse by the end of March. We then decided to close for good. We had a lift that was serviced by Otis for many years. The contract with Otis was cancelled by me to the end of May 2020. They continue to debit the account still every month even after they stopped servicing the lift in June. Their accounts department is not helpful at all and no one seems to be interested to stop the debit order. As the debit order is very old even Standardbank seems incapable to stop the debit order. At Otis no one is taking action to resolve the issue