Why doesn't my mother's side of the family give a damn about us?

I mean they don't give a shit! My dad tried to tell us and he is right once again. Ever since my mom left the family, our relatives have gotten distant from us. It isn't fair. When I tried calling them, it always goes to voicemail. They NEVER call back. When I asked about my mom, they don't respond. They talk to each other. They never call our brothers or us. I told my friends I have the perfect family when I was little. I thought family was forever. My oldest brother told me that not all family is forever and sometimes our own relatives can be our worst enemies. There's some we don't talk to.