I saw the video "Somebody That I Used to Know" by Gotye on YouTube, and it occurred to me that when he says she didn't have to change her number, she definitely had to change her number.
I still have a number with a TX area code seven years after moving because changing your number and updating everyone who needs your new contact information is a huge pain in the ass.
Furthermore, if she changed her number, that means that just blocking his number didn't work. Which implies that he must have kept calling from different numbers as she blocked them.
If she changed her number, I'll bet that her best friend had been trying to get her to call the cops for weeks.