Harassment and Bullying by Cartrack

I installed 2 Cartrack systems. I then sold 1 car. I informed them that I wanted to cancel the contract. They gave me a termination amount higher than the total payments outstanding on the contract. I requested a calculation, but this was never given to me. I told them I would pay when they gave me the calculation. Then the bullying and harassment started up to 15 calls a day including Sunday morning. Every time they phoned they wanted my ID number. I told them that I was not prepared to give personal information over the phone. They then hang up. I told them that they must find a way to speak to me. They phoned me, but I needed to proof my Id without any proof from their side. They then suspended the service on my other car, and put through multiple debit orders without authorisation. I then went to the head office in Rosebank to sort this out. After a very rude and undignified interaction in the reception area, I insisted on speaking to a supervisor. With a professional person, the matter was settled in 10 minutes and payment was made in full and final settlement. On my way back Cartrack phoned to harass me for the outstanding amount. I overlooked this as it was the same day and the system needed updating. The next week SMS and what ups was send again. I phoned and they apologies for not allocating the payment. This is now the second week after the payment and the harassment continues. I phoned them this morning to complain over the treatment I am receiving, they promised to come back. I have since received 5 calls from different people to collect the money, but no return call. I have to explained to every single one and then they hang up. One person apologies. They now asked me for proof of payment when I paid by Card in their offices. I told then to do their work. This is the rudeist unhelpful bunch of people. I am involved in a company with a small fleet of 10 vehicles we will not use them.