Bully Issue, HELP!?

There is this boy from my school who has recently taken to full on insulting, abusing and literally bullying my friends and I. What's most hurtful about this, is that it is unprovoked, and we have never done anything wrong by him or his friends. He has become almost brutal in his insults against us, and we have had enough. We confronted him about it, big time, and made him feel really alone and worried about us....Good. If he does stop when we see him more, that's all well and good, but what if he doesn't? If he doesn't stop, how can we get the message across even further?