help, my sister is being harrassed

AMR • on a weight gaining and yoga journey... one day we will be a family of four 🙏🌈

I wasn't sure where to post this. my sister and I have a phone plan w ATT. her boy friends ex wife got her number and started harassing and threatening her. we took all that to the cops and got her a new number, well, the crazy bitch got her number AGAIN! she's sending her hateful texts and voicemail, telling her nasty and scary and threatening things. she's nuts. what can we do to make sure this bitch doesn't get her number again? how can we make sure it's unlisted? or any other tips and advice, thanks! crazy woman lives in a different state, but she knows where my sister lives and works and even applied for a job where she works!!