Not disputing that name calling is upsetting - kids can be very mean to each other.
However, I think it's important that children learn that parents are not the sole point of authority and if something happens at school, should be encouraged to trust the teacher to deal with it.
Obviously if teacher is not sorting things out that is a different issue, and the parent needs to step in.
Teacher friends I have often say that parents are too quick to complain about an incident their child mentions, when it has already been dealt with in the classroom.