Over heating

I own a 1999 chevy cavalier 2 door coup. 2.2 ltr. Since I bought this car brand new it had a tranny problem that required replacement in the first 6 months I had it and at about 70,000 miles I had to replace the alternator. Other then that this car has been a peach. It now has 94,000 miles. I took this vehical into a quick lube that I had taken it to before just for an oil change on this last saturday. They told me the regular speel, I needed to flush the radiator and the tranny and that the air filter was dirty. I told them not to do anything that day but change the oil. They did so and I drove it home about 4 blocks. I had planned a trip the next day to portland international raceway because I had won tickets to participate in hotlaps. I never made it. 20 miles from town the car started to really get a high temp reading and the radiator light came on. I pulled it over immediatly and got some coolant and water to add to the radiator thinking it was a little low because of the heat. It was empty. Bone dry. They had drained all of the coolant and never replaced it. With out my permission. Now the car is over heating and I cannot figure it out. I have water flow and I replaced the thermostat, to no avail. What do you suggest?