FWIW, one of my best friends has CP. She may be a bit kooky (why else would we be friends?
), but that's her, not her disorder. She's not a saint for having CP, and neither is Ex-GF. Ex-GF needs to be told ONCE to stop calling, and then BF needs to stop answering. He's not doing her or you any favors by putting up with her cutsey, territory-staking phone calls, and he's not being rude by telling her they need to stop.
If I had to guess, I'd say she's absolutely calling on purpose, especially if he's told her you're coming over. What better way to interfere with an Ex's new relationship
than to have the new GF hearing "I wuv you!" coming from the answering machine in another woman's voice?
ETA: Just saw your update. Good. You may need to brace for escalation from her, but he's done the right thing.