Nothing like a knee jerk reaction. If my mail is late I go right to the postmaster general. First, do NOT go to the princi-PAL. Follow the chain of command. Request a conference with the teacher, because, gentle reader there are always two sides to every story. If it is allowed at your school, bring your child to the conference. Ask if there is maybe a bully in the classroom or school that your child is afraid to reveal for fear of retribution.
I'm sorry your friend Susie got shoved INTO a closet. That of course is unacceptable.