Dealing with rude cousins?

How do I deal with rude and disdainful cousins? I have been nothing but polite and nice to them, yet they snub me and treat me as though I am not worth talking to. For example, I actually sent my cousin a message on Fb the other day, via chat, and she actually cut me off mid conversation, without even saying, "talk to ya later"etc...I thought it was so incredibly rude. Yet when I looked on her Facebook page, she was being friendly with other people. She's not the only cousin who has treated me this way. I rarely message them, so it's not like I am bugging them or anything, and of course,they have never sent me any messages..So, should I delete them from my Facebook "friends" list or just ignore them(which is hard to do, because I have to see their pictures on my Facebook page. I did delete them from my news feed, so that has helped. I am just so disgusted with the way that they treat me, and I wish that I could either tell them all off or show them that I am not the loser they think I am. Any good,helpful suggestions?