TELKOM MOBILE CANCELLATION

I cancelled my contract with Telkom Mobile on 16 March 2017 with their preferred method (complete a form and email it to them). To date 18 May 2018 it has not been cancelled and every month they debit my account and I reverse the debit order... I have emailed them, spoken to numerous people and re emailed everything but still no luck! What do I have to do, to cancel this junk? I do not even have the sim card anymore!!!!!