My ex is scaring me, what should I do?

I broke up with this guy a couple months ago because I heard some terrible things about it from other people (violence and other things) that I didn’t know about. Almost immediately after today ended things he started stalking me and threatening my brother, friends and me. He told me that I would regret what I was doing. He constantly contacts me through email (I blocked him on all platforms including calling and texting) and told people I know to be careful of him. I have told him to leave me alone, but now he keeps asking if we can get back together. I don’t want to be with him and honestly being in the same room as him makes me nervous now. What should I do? Keep in mind I am a junior in high school, so please give me realistic advice.
My ex is scaring me, what should I do?
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