Fortunately, I've not had this problem.
There are negative people everywhere. You see it here often enough. The people seeking attention by attempting to degrade another, then claiming they are the victim. They need meds.
You need to keep all the messages, like Leigh and others have said. Keep them, you might need them as proof.
As rough as it sounds, you need to change your number. You might consider changing your e-mail address as well.
If you live in close proximity to her? If it is that bad? Consider moving.
Like Wild Woman said, if you change your number, do not give it to anyone who has contact with her. As we saw the other day on here, people can pick up others phones and do things when they have walked away. If she's that desperate, she might find a reason to use another person's phone to get your contact information.