What should I do about this situation with my ex?

Long story short, I spent just under a year with a guy who is the devil incarnate. He was mean, nasty, abusive, and a cheater.
We broke up almost 2 years ago and he’s still bothering me. Short of changing my phone number, I don’t know what to do. He still call and texts all the time, even though I have not responded to any of it in over a year and a half. I block his number, but he just uses somebody else’s phone to try and get ahold of me.
He doesn’t threaten me anymore, so I can’t file a police report.
It’s just getting to the point of being ridiculous and I don’t know how to make it stop. I think that texting him back and telling him to fuck off will only encourage him.
Any suggestions?