I remember at school a few years back, I stammered on my name when a new teacher asked me who I was. She asked if I had forgotten my name and the whole class laughed. I went home and cried. Things like this are tough, and your situation sounds a whole lot worse than mine was. I guess you could have a quiet word with the ringleader of the group so they can speak to everyone or try and make it known that it is not ok for people to behave like that. It was clearly very hurtful, I don't understand how they didn't see that themselves.