Why do my family treat me like this?

To start, this has been going on for years and nothing has been done about it. As a child, my uncle and his wife would always say that I wasn't part of their family. My cousin used to corner my sister and tell her that she had no connection to the family whatsoever. They always treated us as if we were just nuisances and that we didn't belong at all. Our cousin basically bullied us and her parents pushed her to do so. We never did anything to them and there's no reason to be so horrible. The other day, a relative was visiting and I went to see her. To my surprise, my two aunts (who I didn't know every well) were so nice and treated us like family (which was quite stunning considered the amount of torment I went through in childhood with other family members). Then, my cousin called and was obviously annoyed that we were visiting her and had to, once again, take over the entire conversation. She used to do it as a child and she's an adult now. It was horrible to be completely ignored and have no one really take notice that they were being so nasty. They would turn their heads whenever I came up in a conversation. They're being ridiculous and I'm absolutely sick of it.

I know it doesn't sound like something to get upset over, but a lot more had happened. They actually turned my half-brothers against me and my sister. I'm an adult now and I feel that something has to be done but I'm not quite sure what I can do. Is it some sort of jealousy or just being spiteful?

I don't count these people as family since they never treated me as such.

P.S. I'm sorry I went on and on. I'm just a bit upset about it.