Tracker - Inability to fit a tracking device which led to a truck being stolen

I have a major problem with the service I have received from tracker.

I activated my policy with tracker on the 8th of April. Tracker promised to fit in the device on the 8th of April. They did not install the unit. Tracker called the sales person at truck store centurion and told him they could not come on the 8th of april, reason is unknown why they could not install. Tracker technician rescheduled for Monday the 11th as he would not make it. On Monday the 11th of April 2022 the technician called to confirm that he is at our premises to fit he tracking system. The sales person at truck store then directed him to the workshop (SAC) where they were getting the truck ready and explained to him that we have arranged for the workshop to give him time to fit the tracking system. Where after the sales person did not hear anything back from the technician, taking it that the system was fitted.
I have an official letter from Truck Store SA stating what happened.
The truck was released from the dealership. Days later I called tracker asking for the login details for app. I was told that the tracker had not been installed. The technician, went to the dealership to fit in the tracker however did not say anything to the sales person, he just left without saying a word.
A few days later the truck was stolen. If tracker had installed the device we would have had a high chance to track and recover the truck however that could not happen because of tracker.
Our insurance has asked us to request a letter from tracker stating what happened however tracker now does not want to provide me with a letter detailing what happened.
I have requested this letter and i was promised I would receive it however it however it has been over 7 days now and I haven’t received anything. Tracker is running away from taking responsibility for their fault which has costed us so much. We cannot complete our claim from insurance because tracker has not provided us with a letter.