Unauthorized Debit Orders

In March 2023, I changed my debit order to EFT payment with Vodacom permanently. 3 months later Vodacom decided to restart the debit order. When I contacted them, all they had to say is that they don't know who authorized it and that it cannot be cancelled. From June 2023 till March 2024 Vodacom has been debiting my account without authorizations. Now they have the audacity to charge me a debit order return fee (Note my account is paid up to date and I returned debit orders as the amount on my Statement and the debit order amount does not correspond) When you contact Vodacom, they do not give you all the details, or they "don't know" and make you calculate the invoices on the statement via a calculator to see where the difference comes in, like really? It took me going into a store to find out I have been charged for debit orders returned, but they have no authorization to debit as the account was changed to EFT payment. I really give up with these people!! Slowly but surely cancelling contracts as they come to term.