>>9 AND/OR, go to your ex's house and speak with their parents (only if they're not the over protective type). Try to aim for the parent that's your gender. (If you're a girl, go for the mom. If you're a guy, go for the dad.) It's best if you find a time that your ex isn't home to do it. Explain the situation to them. If you're a girl, you should definitely try to cry. Be as pitiful as possible. BE AS BROKEN AS POSSIBLE, GODDAMNIT. (Unless you're a guy. Guys sound better when they're stating facts rather than being emotional.)
Once you're done with that, if his/her parents don't do anything, explain the situation to a counselor and have the kids shut up. In either situation, you should try to get a recording of the kids bullying you. (The best way to do this is to buy a pocket MP3 that can record audio. They're like 15 bucks at your local convenience store. Maybe. Depends on where you live.)
I cry spontaneously (and often unintentionally), so I'm not the best example, but I know there's some magical way to make yourself cry. Hopefully the situation will be bad enough for the tears to come naturally.
Hope everything works out well enough~