It's a difficult situation.
if it's restricted to online, report to Whatever admin is available and block them everywhere. Unfortunately this happens and it's not on you in any way, but it does and the only way to reduce it is to report it.
If there is a physical component to it, someone you have contact with, it's a different situation. I know how hard it is but do reach out to someone you trust, let them know you are worried, they don't need to know why if you don't want to tell them.
ignoring the individual is a start, don't ignore the situation, if it's biting at you you need to talk. Might be to a friend, a professional or online like this... it's a step in the right direction. Look after you, you'd be surprised about who will understand.