Can not cancel debit order

Why can I not cancel my debit order with Telkom??? All other companies accepted me cancelling my debit orders with them to become a cash payer. Telkom refuses to help me. Why can I not pay my Telkom account via EFT like I do with all my other accounts? Your Team Leader Sibusiso said to me Sorry, but he can not help me as they WILL still debit my account every month, as I do not have a choice or an option? It will surely be better to cancel my contract with Telkom and rather support other companies that is much more helpful.