Cant close DSTV account

I immigrated in September 2019 and asked for my DSTV to be disconnected from October 2019. I sold my decoder to someone on Gumtree and as per DSTV's instruction, I gave the user a change-of-ownership form (filled out). Since then DSTV have been deducting money from my account without my permission. I phoned DSTV from Germany last year and noticed that all the verification details I was asked, is exactly all the details on the form I gave the user. He obviosuly never changed the decoder to his name and now have my ID number, Name and Surname, Address and telephone number...essentially giving the new user all the detail he needs to phone in and pretend to be me??? This makes no sense...and now I have some guy activating my account every month, having to cancel every month and try my best to reverse the money from my bank account. I have now instructed my bank to stop the debit orders, but somehow its happening again...I have spend countless minutes on the phone, spent how many euro's phoning DSTV, but cancelling your DSTV account seems to be impossible. I am actually out of options. If DSTV could contact me that would be great, cause the phone magically gets disconnected every time i reach the cancellation department...this is very upsetting. Replies on social media goes unanswered...