Read your phone instruction book as all are different. Mine I can block texts but not phone calls. If you want someones number permanently blocked contact your service provider and they can do this for a charge. Personally I would just ignore their calls and let them run up a bill. They will not even know if you have seen them. Another thing to do is swap phones for a few weeks with a friend and when they hear a different voice each time they will hopefully give up. You can report them for harassment if it is really bad.