Poor communiction, failing to acknowledge my cancellation

On 27 July 2016, I cancelled my account with Chubb. I was told to send them an e-mail to confirm and I did so. I then had them still taking off the amount every month for another few months. I phoned again and was told to send them another e-mail which I did. I also went to my bank to cancel and block the debit order. I had more calls from them asking me to pay the arrears I moved away from Witbank end of November 2016, and still the accounts are coming to my postbox. In February2017 I send them another e-mail but nothing changed. I still get these accounts asking me to pay the arrears. What will it take to get them off my back?