A MISSION TO CANCEL MY ACCOUNT

This was a very good company up until something happened and I have no idea what. I have emailed them a cancellation on the 09-12-2019 to cancel my contract. I have send them 15 emails. I have disconnected the dish etc. At the end of Dec the same debit went off. I phoned in and spoke to the accounts and they have "stopped" the debit order. I received a cancellation letter on the 17-01-2020 filled it in and send it back to them. End of Jan the debit went off again. I then phoned in and the accounts people said that they have cancelled my debit order. Today 18-02-2020 I received an sms that my account is at rears. I phoned accounts again and they confirmed that my account is still running. How the hell do I cancel my service with them? What do I do if they want to black list me etc.... This is insane. I would not recommend them at all.