Bike damage aside, it looks like you may have to arrange a meeting with the head or understudy and go down there to bend some ears, ive always found this works alot better than a phone call as its easier to fob someone off on the phone, then when you get to your meeting emphasize the verbal bullying and try to get that sorted before mentioning the bike damage,
I had a similar nitemare with my daughter and ended up getting the police involved, they were very good tbh as things were escalating , but i did end up visiting 1 lads parents to get things sorted.
Good luck.