How do I unmask a private number?

There's a private number who I know is a lad in my class calling me to make fun of me and I really want to call him back to make fun of him. Unfortunately he keeps his number private so the only think I have on him is the call logs. I have an irish phone number so I can't use trapcall or any american 3rd party apps. I know I could block him but I really don't want to, he's harmless and I just want to spook him. I'm not planning on doing anything else. Thank :)