heating system + service engine light was on

My 2 cars have been serviced by them in the past 5 years... They were really good in the beginning, however the last few times we've had a very bad experience at thet place. My last car service was last week... I picked my car up and the service engine light came right back on. They wanted to charge me additional $100 to put it back on the computer! That was on top of $900 that I jsut paid to fix my heating system. ( first time they called and said that the motor needs to be changed and it will be $400, however, that didnt solve the problem, so they had to change the amplifier for additional $425)