Loads of smartphone apps will block numbers.
You also have to wonder what kind of person would put up with creepy texts for three years and refuse to change numbers.
I agree with this tbh. 3 years is a long time and to refuse to take the easiest option to stop it makes me wonder if there's more to this story than has been let on.
The police probably won't do anything at the moment, I'm assuming because she hasn't asked this stalker to stop contacting her. It's only from that point if he continues that they could intervene.