Former boss won't stop calling and harassing me. What should I do?

Hi guys, I've got a really annoying and stressful quandary. I quit working at my last employer because my boss was extremely hostile and higher ups refused to address the situation. In short, this was a manager who would do things like offer vague threats to fire everyone over new policies she made up pretty much every week. Even when meeting goals and following corporate policy, she would put employees she disliked on "improvement plans" and eventually fire them for not meeting vague goals that could not be met. She would fire anyone who gave a two weeks notice. She gossips about employees to other employees behind their back, including revealing information that was meant to be confidential. Talking shit about former employees, etc. We all know the type. I finally had enough and quit. I planned to give a notice, but I knew I'd be fired if I did, so I didn't. I didn't want to be treated like garbage for another two weeks even if she did decide shed rather keep me around to do so. My former manager who also quit because of her and I both emailed our district manager detailing the hostile environment but this was also ignored. Her boss just sent it to her and told her exactly what was said and who said it. I know this because other employees still there have told me she has been asking for information about me and has told them information of incidents I hadn't told them that were included in my email.

The reason I'm posting is because after I quit, I got a threatening phone call from her using a "blocked" number. I have an app that records my calls which is legal in my state. It also unmasks blocked numbers, so I know it was hers. She threatened me saying "you fucked up, bitch, you should be worried, bitch..." For several minutes. She disguised her voice (badly) but she will not stop calling. 5 calls today, and I have proof. What should I do? I took a lower paying job because I couldn't take the stress anymore and it's hard. If this goes on, what should I do? I feel like the company is being negligent in refusing to address this situation. I liked the job and still have good relationships with everyone else there. I wouldn't have left except for her.

Thanks a lot for any replies. I am in North Carolina.