Telkom cancellation nightmare

Last year October 2017 I went online to cancel my month to month contract with them I followed the online process and there after received a ref number through email that stating my cancellation is being process about two weeks later I phone in and ask whats happening is the account being closed then they said there some money outstanding and I need to pay it so i said fair enough I will do so and then I asked the cancellation ? then they said its being processed and should be through any time now . After that I changed bank accounts and never saw they still trying to take money off but anyway a almost a year later the debt collectors starts phoning me and says I must pay and then I explain it to them what iv done but now they phoning me every day and then I have to explain the whole thing over and over to them they keep asking for a cancellation form then I keep telling them its been DONE ONLINE I got the reference number telkom never cancelled the account . I dont know what else to do anymore they keep harassing me now every day they dont get in there heads .When you phone telkom they say I must pay period and then when you ask if you speak to a manager then you get told you may not.