2015 fusion se temperature sensor fault

My husband noticed the coolant level was low, so he added more. After work he started the car and it started ok but would not run. It stayed in idle and would not accelerate. We had to have our car towed to a dealership. Dealership called him next day and he related story. They then proceeded to diagnose the issue. First called and said it would be $110 to start. Then required an additional 3 hours for a total of $440 to finish diagnostics. At this time they decided to remove and replace intake manifold, Air control valve and engine temperature sensor and do an oil change. At no time was authorization given for anything but the diagnostics. Now they say that the coolant must have evaporated as they found no leaks? I thought it did not evaporate in a closed system? We top up all fluid level as necessary at every oil change. We have ALWAYS used synthetic oil (which they did not) and have stayed on top of any issues that have arisen with the car. It is a 2015 model, I see recalls for the 2013 & 2014 model years for this exact problem. No recalls for the 2015 model year. Car is at 109,000km 9,000km over the warranty period. As I have been told that the issue was the temperature sensor malfunctioning I am quite upset that the dealership will not do anything about this costly repair. Has anyone else had any of these issues?