Dealing with gossipy cowards?

I had to do a group project this term with five other people on my course, all of whom already knew each other. I was considering going with a group of friends instead, but the experiment my group wanted to do appealed to me much more and I'm acquainted with one of the guys in the group so I assumed it would be fine. Long story short, they were nice when I met them but they've treated me like complete crap as soon as it was too late for me to pull out. They haven't said outright to my face that they dislike me, but I would have preferred it if they had because several times I've overheard them saying stuff behind my back for no reason: everything from "she's shockingly ignorant" to "she's nice but not much there," to "is there no way we can throw her off the project?" I have tried confronting them about this a couple of times and they've outright denied it, but it's obvious they lack any respect for me - I've heard them laughing about me several times before they've spotted me in the library, for instance. There's no good reason for them to behave like this: I've put the most work into the project, get the best grades and am obviously not "ignorant" and have always been polite to them though recently I've just shut them off and been cold and indifferent because it's useless putting in any effort to make friends. They also have a complete lack of social skills: even at the start when I'd walk up and say hi they'd often not reply or say "helloooo" in a weird sarcastic tone of voice as though they were too tired to make the effort to do so properly. They don't have many close friends besides a group of similarly catty people, but they are acquainted with some of my friends and I've heard they've been spreading vague nasty rumours about me. Thankfully we are submitting the project before the end of this week so I won't have to deal with them again, but I don't feel like I can just let this slide. I've been pretty cold to them recently but I can still hear the gossiping going on every now and then and I don't want to just ignore it and forget about it. What's the best way to have a word with people like this? I don't care if they deny it any more, but I don't feel I should just let them get away with it. I am the only girl and the rest are all boys (but not your stereotypical "lads," if they were they wouldn't be behaving like this) if that makes a difference.

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