umm, i think there is a little more to this story than what you are saying

#1 if they sold you a car without cats on it why didnt you just ask for your money back?
i mean i would be leary of what else was done to this car.

#2 how can they steal a cat back exhaust when there is no cats to begin with?
if they had to reinstall cats to your car then that means the original pipes were probably welded in place
once they removed the old cats.
so my theory is they had to install a complete new exhaust from the engine back so it all BOLTED together
as the car would have come from the factory.