Impossible to cancel a contract with this copany when you don't want their services anymore

I have been trying to cancle my contract with this company since 29th January 2020. I have received telephonic and emial confirmation that they have received my request but it goes no further. They keep telling me somebody will contact me. nobody contact me but I don't want to speak to anybody anyway. I have very clearly stated each time that I am cancelling my contract and they must cancel the debit order. Once I even received assurance that the debit would be ancelled but it wasn;t and they just keep taking money from my bank account. After I had given notice I was cancelling and told them to cancelt the debit orer, the debit odrers became theft. How do I cancel a contract that the provider refuses to cancel? How do I cancel a debit order that the ***** refuses to stop? The only thing I can do is to close my bank accounts and reopen them so that they no longer have my account details. Do i really have to go to such lengths to stop them takng my money every month after I have told them to cancel?