hacker harassing me and my friends need help

I have a hacker in my realm, and they are stealing from us, griefed my friend bass, and now threatening the realm and one of my other friends too. they did this all in vanilla survival(no cheats at all); I am even afraid to turn the realm off of perfect because I don't want them getting end crystals. I don't know who to call for Microsoft or Xbox to get them off the realm for good. I have shot down the old realm and made a new one with the same world and they still hacked there way on.

1. they hack into the realm so can't ban them or report them and are hiding their name and are invisible too. they are now hacking in items like elytras and hitting my friends, leaving signs saying "ready" "I am real", and other things as well. they are harassing me and my friends and I am afraid that they may delete the world or worse please help
   
   
   
   
   

:)