I'm not an HR or police expert, so I can't definitively answer your specific questions. But here's what immediately came to mind....
Have you asked your ex about it? I would go straight to the source, in person. Let him know what you're hearing, then calmly ask him to stop. It's too easy to ignore a text or email, and when you're standing face-to-face with him, it makes you a person (someone he once cared about enough to have sex with), and not an object for ridicule.
It doesn't change the fact that it's now out there, and you can't control who is telling whom. For that, I am sorry. You just hold your head high and walk tall.
He will lie. He told me he left his ex GF for cheating on him again so he came crawling back to me, I found out yesterday they are still together but of course after she found out about us being together and having sex she went off and he denied everything , she showed me all kinds of screenshots of text messages including from the night he was with me in a hotel room and told her he could not message her anymore that night because he was at the police station in trouble for selling his car and not getting it out of his name in a certain amount of time. He told her they were holding him overnight for it and taking his phone away.
His ex and I found out alot of stuff last night after talking and wish we had talked sooner, the guy is a pig and lied to us both. He was screwing with her claiming we had broken up then he was screwing with me claiming they broke up. He has been bouncing back and fourth cheating on us with one another