How can I work through this?

My nana passed away in April this year. She had custody of my neice. I lived with my nana and neice for 3 years before my nana passed. I wasn’t living there when she passed though. So the neighbors took custody of my neice. Bc her family could step in to take care of her. She is refusing to let me see my neice. She makes up excuses everyday. As to Why they can’t meet me. I’ve seen my neice on video chat one time since my nana passed away. And now she’s posting that my neice wants them to adopt her. She’s 9. Is there anything I could do to get visitation rights. She’s not biologically my neice. My nana is my moms stepmom and my neice is my nanas great neice. But I have pictures to prove I’ve always been in her life. Idk what to do. It’s killing me not seeing her. She was like my child. Any advice would help.