I'm so sorry to hear this ballet bun, how awful for all of you.
I would agree that escalating to Head of Pastoral or School Head is the next step.
Our experiences were that:
1) there was a huge difference in competence between different house parents in terms of skills at dealing with such issues
2) if any issues (pastoral or dance) were not dealt with satisfactorily then escalating to Head was only way to get it dealt with.
3) Agree there is often poor communication between pastoral, dance and academic.
If you think bullying is happening do you have a copy of the school policy?
Are there any room allocations that may help for next year?
Wishing you all the best xxx