So what do you do when someone has a vendetta against you for something that happened ages ago?

So this person , I’m not going to say who it is has it in for me. I’m serious. They are a complete jerk to me and there’s no way I can fake that I like them. Well something happened today that was the tip of the iceberg and I’m at my wits end. So what do I do because i CAN’T TAKE THIS? This is borderline harassment . Oh by the way I did report all the incidents and it didn’t change anything. p.s. I’m not someone who’s looking for attention.