Dont know who this number is. try to ring it back and I dont even get a phone ringing on the other end, it then tells me there is no answer.

It's a generic voip service number. My friend has one and uses it to call me on my mobile.

They call me and know everything about me, age, where i live, school and even my friends. but when i ask who it is they put it off or either hang up. they also call me multipul times!

I believe it is Optus