My half-siblings refuse to have anything to do with me, how can I get over the loss I feel?

Basically my mom and dad dated, she got pregnant, he wanted her to have an abortion, she chose not to, he got mad and still won’t have anything to do with me. He married someone else 2 yrs later, had 3 kids. When I was 18 I contacted them on my own, they had no idea I existed, we met, they talked to their parents, and since then none of them want anything to do with me. It’s hurtful, it’s hard to understand how people could be so cold, and I’m tired of trying, but the idea of not trying hurts too.

*One sister friended and de-friended me (not vice versa) on fb a few times, since then she blocked me. The other two are on fb but we haven’t friended each other. One said she felt bad but didn’t know what they could do about it since their parents weren’t thrilled with us talking.