Wazuans, this is a very serious issue!
This problem started in March 2011, its now well over 3 months since this piece of waste started irritating me and my wife. Luckily, my SAMSUNG has in-buiilt applications that can block some callers.
For the sake of my wife, her Nokia can only allow all calls baring and cannot allow the user to set the private/unknown caller's ringtone to be silent, since there is no number. This has led my wife to switch off her phone for most of the days.
How can u help?
Receive with simplicity everything that happens to you.” ― Rashi