It is possible that what the opposing insurance company is trying to say is "this is not our problem." If they, just to theorize, sold this insurance policy with limitations - Insurance Company A provides insurance on company vehicles only when driven by authorized operators, and only when certain rules are adhered to (like rig/driver has to be off the road for a certain amount of time between shifts). I have no idea if that arrangement would even be legal. But it's possible that what the insurance company is saying is that they do not provide insurance for this event - unless, perhaps, this was a different truck, ma'am?

If that's the case, your insurance company is probably going to need to file suit against the trucking company. But they should still cover your loss in the meantime, no?

You really need your insurance company's involvement.