I took my car in because the heat was not blowing ...

I took my car in because the heat was not blowing hot. I was told it needed a thermostat, so I had them replace it. After I paid for it I checked it out and the heat still blew cool air. The guy who worked on it had left for the day so I had to leave it overnight. That was a wasted 1 hour roundtrip to come pick it up. Very frustrating.