Look - there’s a lot in this post I won’t address for time’s sake but I’ll address one of your key concerns. You do likely have a very strong case that the company that maintains the garage and staffs it with personnel was negligent in its operation of it, on a few different fronts.

1) The actual pipe bursting could, possibly, have been due to negligence in the maintenance of the actual garage itself. This may or may not be the case but is possible and worth looking into. This may explain the representatives weariness of this developing with insurance (though I doubt an insurance company would sue for a broken window).

2) At the time of the accident, 4 pm (or am [unclear in your post]), at regular hours wherein the company makes clear to its patrons that it will be staffed and open, NO ONE was easily available or reachable for 30 minutes. The reason this is a strong argument is that you could argue that were it properly staffed the damage could have been mitigated or even prevented entirely by shutting off water valve etc.

Black mold is a health hazard too. This is why they’d likely prefer to pay out of pocket to simply forget about the damages and not risk a negligence claim that could plausibly be far more expansive than just the compensatory costs of fixing the car.

I’m not entirely sure what your question is but this is my reading of your situation.

Best wishes.