Officially realizing I should go completely NC. I need support

(⚠️TRIGGER WARNING: CHILD SA⚠️)

I've posted on here previously about this situation with my family. Quick backstory, when I was 14 I was molested by my older cousin at a family event. I told my mother about it later that day and her first reaction was to not believe me. My entire family heard about what happened and said "just keep your distance from him" "he didn't mean it" "he's family". It wasn't until I was an adult and moved in with my incredibly loving and supportive partner, that I realized how fucked everything about that was. About 4 months ago when my mother and grandmother were visiting me, I decided to bring up that time and talk about how the situation was handled and how it made me feel. They responded with gaslighting and manipulation, saying "I thought you were over it" "I don't know where this is coming from". Since then I've had multiple phone calls with my mother, attempting to gain clarity and discuss various things that happened throughout my childhood(both my parents were also physically and emotionally abusive). Since then, my father and brother have completed cut me out of their lives. I've heard nothing from my grandmother or grandfather, except for them sending family pictures and about how they love me. Last night during this conversation with my grandma I just broke down. It's infuriating, how can they not see how WRONG it is? I was a CHILD. I lost my entire childhood. I'm so incredibly exhausted. I'm only 21 and I feel like I'm 80. I feel like I've experienced enough that life and the world has to offer, I just want to go live somewhere where no one will bother me.

TLDR: I feel like this is coming to a point where I need to go completely NC. What is your advice and how did you do it?

If you read this far, thank you so much. I really appreciate the support.