How can I get my Facebook account back from my ex

My ex has taken over an old Facebook of mine. He went in, changed both the email and password to his, and I can’t get back in. He’s also been claiming to reply to messages and says he will make posts too but I have a friend who is still friends on the account and is watching it for me.

Is there a way I can have it taken down? Or a way I can get it back or contact Facebook to let them know what’s going on?