Annoying music teacher

Im in yr 9 and in school we do music, but the music teacher is so annoying. She blames me for things i didnt do. Like, yesterday we had to play a song on the keyboard (we work in 2's) so i play the right hand and my mate plays the left hand. K, now my mate goes to school band and plays trumpet, so the music teacher is allways biost to ords him. I play the keyboard and im grade 7 but my music teacher doesnt believe me. So she pickes us to play the song to her and we do it. Then she says 'YOU DIDNT PLAY ANY OF THAT' and i said 'I did' and then she sent me out of the lesson. She then gave me a 30 min for 'Not playing the song and Answering back in a rude way'. Everyone saw that i did play the song so i went to head of year and he said i didnt have to go to the dt and he would speak to the music teacher!!