Cartrack Messed Up My lights and Wont Admit

I had a telematics unit on my car and according to Cartrack the unit no longer had a recovery warranty which was one of the requirements on my insurance policy. So I had to Install a new Fleet unit with a recovery warranty.

They sent a technician to install the unit on the 30/09/2021, the same day after the installation, my lights were out on the left side. I called them and I was advised they will send a senior technician to check. On Monday(04/10/2021) the technician, an arrogant and condescending guy, came and without even checking the installation that was done by the 1st technician concluded that the issue was the car fuse which had blown up. He put a new fuse and the lights worked, according to him, it was just a coincidence the fuse blew up the same day the fleet unit had been installed and the old telematics unit removed.

I tried explaining to him that it can't be a coincidence but was met with how many years of experience he has with dealing with irate people. As per his suspect findings, the problem was on the car so I would have to pay the R600 callout fee, which I then refused to sign for as I believed the installation of the unit blew the fuse up. And to my vindication, the fuse he put couldn't last 24 hours, yesterday(05/10/2021) my lights were off again on the very same left side. So surely the installation wasn't done properly that is why the fuses are blowing up. But Cartrack won't accept that, my car lights were working fine with the telematics unit so the only thing that happened between my lights working and not working was the installation of the fleet unit and the removal of the telematics unit. Because I didn't agree with the senior technician's diagnosis, I'm being threatened with another R600 callout fee should another technician be sent.