very disapointed

I want to express my disappointment with Netstar .September 2019 I bought a new car. Before I took owner ship of the new car I send Netstar an email requestion how do I go about by cancelling my policy with them, nobody came back to me I phoned Netstar offices and i spoke to a lady she said that I should contact my insurance( wich was Unity at the time. I phoned Unity I cancel my insurance with Unity aswell as my netstar services. Accordng to my knowlede the unit installed in my car belonged to me cause I had the unit for more than 3 years. Know I`m receiving phone calls from Nestar That Iowe them R297 Im not sure for what.??Then today again I recieved another phone call from a very rude and unprofessional screeming at me as if im a retart or someting. Netstar staff didnt do their jobs now they are terorising and threatening me. Why havent they disclosed all information to me regarding cancellation and why havent they sorted it back then. And if the unit are still active why havent i recieved any phone calls just to make sure everthing is ohk like in the past while I was still one of they clients??? Im not an idiot to sign a new contract with somebody else knowing that my exiting contract hasn`t been cancelled. I need Netstar to sort this query out ASAP.