I'm so sorry to hear that, how horrible for you! At the start of Uni people are so desperate to fit in that most will just go along with what the crowd is saying, it's likely at least some of them didn't even think that about you! Either way, they don't sound like very nice people - they clearly aren't worth your time and energy. If it were me, I would probably not want to have to keep living with people who were so two-faced and I'd try to change accommodation (as someone mentioned, could you contact student union?).
The great thing about Uni is that there is such a HUGE variety of people, you will find some amazing friends who are lovely in the end. I personally felt very out of place in halls but met my best Uni mates in 2nd and 3rd year who are just awesome. If you can't move halls, I'd advise joining clubs and societies that truly interest you, because that is where you are likely to meet like-minded friends. If you don't find your people for a while, don't worry, it took me a long time, but you will meet some great people eventually, I promise!
With regards to those flatmates, it's hard to advise what to do without knowing you. I don't think confronting anyone will help - sounds like they are the type to get defensive and *****y instead of feeling guilty and being kind. Maybe you could become close friends with one or two of the other 5? Obviously don't smother them (I say that in case you feel insecure about making friends and therefore go overboard). Maybe you could 'hone in' on someone with whom you naturally gel and who seems to be lacking in confidence a bit themselves /could do with some security through friendship?