I am getting calls from a obsence "private user", how can I find out who this is or can you block private user calls?

This is very difficult. Many of these calls cannot be trapped by the phone carrier.

Just don't pick up - eventually people get tired and bored and start calling someone else. Use your caller ID.

Pick up you phone.. dial *77 (or is it *87?)

This turns on - "No Caller ID Block" so... if someone one tries to use *67 to block their ID it will deny them.
So, they would have to call normal... and let you see the # if they want to call

Now, if the number is unlisted... then they can still call you.