How do you block someone from calling your cell phone???? I have Ntelos,,,,?

My boyfiends ex keeps harrasing us and calling the cell phone and leaving silly voicemails and hanging up on me when I answer and blocking her number...I called Ntelos and they said that there is nothing that can do...that they were working on a block feature...anyone else out there have any other suggestions?? we don't want to change our number....How do you block someone from calling your cell phone???? I have Ntelos,,,,?just hang up on her or dont pick it up