Until you're satisfied something is being done, and done to your satisfaction, don't stop. If the teacher doesn't mitigate your child's fears and the events causing them, call the counselor. If the counselor doesn't help, call the principal. If the principal's a bust, call the district. And if the actions are criminal, it's your right and duty to phone the police.
These days, one in five children falls prey to peers behaving badly. Parents must be vigilant, well-informed and prepared to take effective steps to return a healthy, happy educational environment to their children.