Debit order continue going off after its been cancelled 3 months ago

Hello I have cancelled my membership with them the 31 August, they then gave me an option to either pay another instalment or to pay in the claims amount that was still owed. Which I did I send them POP a lot of times, every-time I need to send it to the next person. Then the 01st of November they tried to debit my account with the double the instalment amount so my account went into arrears. I contacted them again on mail sending the POP of the settlement amount and the cancelation mail. I also tried to call them but because they have cancelled my medical aid my number doesn't exit. So I mailed them everyday eventually they send me a confirmation that it was cancelled 31 Aug. To my surprise the 01 December they have a DD of again double the usual instalment. Now I don't understand how you can still try to take money from something that has already been cancelled 3 months ago. How many months are they still going to try to debit my account. This is putting my credit score and my account in a bad status. Can Someone please stop the DO. I also tried to call them but after being on the phons for 7 minutes it just cut off this is after how many times that I am trying to call them.