Some girl keeps calling my boyfriend and we are ALL getting mad about it?

Ok, so my boyfriend is well liked and alot of girls like him, which isnt much a problem because they know when to back off, but lately there is this one girl that found his number and keeps calling him. Ok, so my boyfriend is VERY trustworthy and faithful and would never cheat on me and he is getting aggrovated with these two different girls Paige and Felicia that keep calling him. He usually has his brother tell them he doesnt live there anymore, and other than that he doesnt answer. Today his sister picked up the phone and told him that some girl was on the phone for him, and she asked who was calling and she didnt even say her name, only Is brandon there? again. We dont know how to get them to stop calling and sometimes they call from blocked numbers. Please, Im about to step in and erm, TALK to these girls personally because they are really pissing me off. What should I do to get them to stop???