Please, please, please do not allow this woman to teach your child any longer. Even if you work out your relationship with her, she will take it out on your son. Who knows what she is doing to him when you are not present. If he formerly loved school and now hates it, there is a HUGE problem!
When I was in 10th grade, there was a boy in my class named Ronnie. Ronnie was likeable enough, a pretty nice kid and really smart. It was an honors english class actually. The teacher for some reason decided she hated Ronnie and pretty much made it her mission to take him apart. At first we all laughed when she poked fun, but then she just kept up. Within weeks we were all trying to protect the poor guy. By the end of the school year she turned a sweet, smart, happy kid into a self-conscious, uncertain morose eeyore type guy. He never, ever recovered from her verbal abuse. It was horrible, just horrible.
Please don't let her ruin your son. Be strong. Be his hero. He will always remember that you took his side and believed him and that you took the time to protect him.