My ex boyfriends new girlfriend is harrassing me??? Help!?

Okay so I dated this guy awhile ago, and I've been with my new boyfriend for 2 months. Me and my ex still stay in contact. We talk on facebook occasionally, and text sometimes. He just got with this new girl a week or 2 ago, and now on Fb she gets on his account and starts IMing be a bunch of really weird stalker stuff. Then she says she wants to beat me up, but she only keeps it cyber! haha. She never calls me to confront the issue. I dont have her number so I cant try to fix anything. When I do try to make amends with her, shes just a b*tch. She always calls me a hoe and a skank but I dont wear slutty clothes and I'm a virgin, plus I'm pretty sure I'm not a garden tool. I have no idea what to do, because I wanted a drama free summer! She's my only hater (that I know of) I find all of this ridiculous especially because she's a year older than me, and I'm the only one trying to be mature about the situation.