Boyfriends girl friends don’t like me??

So long story short, my bf’s girl friends don’t like me and I have no idea why. I have tried and tried for the last two years to be nice them but they just won’t give me the time of day. We went to a party with all of them and no one except one talked to me and I expressed how pissed off I am with them. Am I doing the right thing by putting my foot down with them? And any tips or advice on how to deal with a huge group of girls that don’t like you but you have to see them? I’ve asked him to stand up for me with this and he has agreed.