What do you do when a teacher yells at you because you questioned her disipline?

I picked my child up from a school for lunch. He is 7 and told me all 4 second grade cles had gotten in trouble in PE earlier and they all had to walk laps around the playground at lunch recess. So I took him back early so he could do his time for misbehaving. Due to rain, the recess was a movie on the floor in the basement. I walked him down and about 20 or so students were sitting against the wall, facing it, while the others watched the movie. My child quickly sat with the others facing the wall. I knelt behind my child and asked him what was going on. Another student started telling me that everyone had already sat out in PE. So why were they being punished twice? Suddenly the teacher started yelling at the little girl not to talk, I stood up and went over to her and asked if they had already been punished. She yells at me, tells me no and storms up the stairs to retrieve the principal. I told him how rude and hateful she was and wanted to know about the punishment. He said he would check into it and let me know. When nothing happened, I called the superintendents office. Still nothing has been done. Twenty minutes? They are 7 years old. For years parents have told me it doesn't do any good to complain because no one does anything. They were right!