well... there's not much you can do. I've been there, done it.... and I know how it feels.
Now thinking back to my previous experiences, I can't help but wonder why I never just confronted them.
First, ask them why they are spreading rumors about you. It never helps if you get people to back you up and create a war---> it will only make things worse.
If they start saying BS like "Oh, we don't like you" or "It's because you're a total loser" or something then please, tell them to get a life and stay out of yours.
Even if they did start false rumors about you, they have NOTHING to back it up, only you do right? If people doubt you, then tell them to prove it. If they can't prove it, then everyone would know that they're wrong and just starting something really stupid.
I know, it's hard not to think about it too much but please don't put it to heart.
Well, good luck! I hope my answer helps you. =)