Telkom holding my account hostage

I have ACTIVELY been trying to cancel my contract since February 2018. The contract period was fulfilled, so I owe nothing on the account. I have phoned, emailed, Facebook posted and used Facebook messanger on an almost weekly basis to absolutely no avail. I keep getting the same useless response: "please cancel using our app or website". I have used their stupid website to register. The website says I have no products with Telkom. The app keeps saying my account doesn't exist. Every time I email or phone, I keep getting referred back to the website or app. I even phoned their stores in the hope that I can cancel there, but they state they no longer do cancellation in store. So every single avenue available to me does not work. If they literally make it impossible to cancel, yet keep charging me, surely that is tantamount to a ******** action? Is that not holding my account hostage? To top it all off, they then debited R500-odd to my account EXTRA with zero explanation (I have NEVER missed a payment on the account). I have been waiting 2 weeks for a response on this. I am cancelling my debit order with these *******. They must try and come at me from a legal angle. I have saved every form of communication I have sent making my intent to cancel VERY clear.