Terrible service

I cancelled my contract with National on the 19th of Aug 2022 and I received a call from Indreshni on the 23th of Aug 2022 asking me why I want to leave and which security company am I moving over to and I told her it's none of her business. She then send me an email stating that I should pay R515.32 as that is my outstanding balance and there is a fee for the Radio Removal however they noted that if I deliver the radio myself I don't need to pay. Then on the 25th of Aug 2022 I then paid the outstanding fee as requested on the letter I received. On the 1st of Sep 2022 I received an invoice with a Radio annual fee and the monthly fee. I have cancelled then and I delivered their Radio so why should o still pay these people. If this issue is not resolved I am going to involve my lawyer.