Strategy Al,
Phone them and say you may be cancelling the installation. Giving the reason that they have displayed incompetence from the beginning. Which would also be reflected in the installation itself. Consequently resulting in poor reliability.
Watch 'em jump hoops. Allow yourself to be smoothed over and accept the installation. It will motivate them to ensure all is good.
Whichever way you handle it let us know what the results are.
Cheers