Getting an installation appointment is a pain

I signed up with Netstar three and a half years ago, everything went so smooth and without issue. I test the unit as required, and a year ago the unit was not working and Netstar made arrangements to replace it without issue. I WAS very happy with Netstar. After the 3-year mark, and they wanted to fir a new unit. No one called to arrange fitment. After three weeks and three follow ups I managed to set an appointment, gave them a week's notice, booked for 8am. On the phone they told me it was confirmed. 8:30 came and went so I called, and got told I never confirmed, though Netstar never asked for confirmation. They offered me 11am, I explained that it needed to be done by 10am or we must book a new appointment. The planner called me back saying someone could be on site by 9:30, and after discussing it I was guaranteed the car would be ready by 10:15 to use. I explained that I need the car to go to work at 10:15 and it must be done. The tech only arrived at 10, and needless to say it's not ready at 10:15.