I am so sorry to hear this happened. I was a little confused if you locked your bedroom door (with a key or electronic key presumably), how your guests could have got in without the key? Did they break the lock?
Presuming it's against your house rules to use/go into your bedroom and have parties....I would contact BnB straight away - you have 48 hours from the guests leaving - with photographic evidence of any damage to your property.
Also make sure you leave an honest, factual review - so that other hosts considering them as guests know about their behaviour.