Telkom *****ing my money!

I have had terrible services from Telkom. I canceled my internet services with them in November 2018, where I gave them one month notice. The next day after sending the email the internet was canceled. BUT my account was still debited. I lodged a complaint and the next month they debited my account again. I then resorted to going into the bank and having the debit order returned and putting a stop to the debit order. Telkom continues to try to debit my account every month with a different reference each time so the bank is unable to stop it. I am getting tired of having to go into the bank every month to have the debit order returned and for you to hand me over to debt collectors. How do I get Telkom to stop taking my money?