Nestar is not honest in their dealings with customers

This year in April, I bought a second car and I asked Nestar to install a tracker on it as I already had their tracker on the first car. They installed the tracker and also said that they need to replace the unit on the first car as it was outdated. When I decided to sell the first car they did not want to cancel the contract on it. Apparently when they replaced the unit they entered me on a new contract without telling me. Now they are saying that I need to pay a cancelation fee of R2,500. Last time I spoke to their agent I was promised that they would call me back after accessing the recording where we spoke about the replacement of the unit, and as I am saying that I was not informed that I was entering into a new contract. I also was not informed that their service was not month to month but rather a 36 months contract. My advice is never use Nestar, they will do anything to make money and keep you on a contract even though you no longer need their services.