How do you know that all people have souls? Also because it's written in that 200 years old book?

Btw, when I was a child I really "seeked" god because my parents said he exists. But after I read some books that aren't 2000 years old but are about science, I got doubts. And then I realised that god actually doesn't answer. If you pray nothing will happen. Did you ever notice that only prayers get accomplished that can happen by random?