This guy keeps booting me offline

No offense but that's a bad idea, ur ip doesnt change just because you reset ur internet

if you turn off your router for 10 minutes it will be issued a new IP address unless you have a static IP.

if you have a static IP you need to contact your ISP but you should contact them anyway as DDoS attacks are illegal and your ISP are in a better position to take the matter forward with the authorities

block him and report him then reset your internet box to change your ip

report it and block, after if the ddos attack continue you can ask help to your ISP

Please read this page about DDoS Attacks on Xbox (that causes you to be booted offline): https://support.xbox.com/help/Hardware-Network/connect-network/dos-attacks-faq

After you read that, block that guy's Gamertag. That way, you'll always appear offline for him, and unless you are in the same multiplayer match or in the same party, they can't pull your IP to start the DDoS attack.

If the person continues to use DDoS attacks, contact your ISP, as they can then log the attack and report the person to the police, as DDoS attacks are illegal in most countries.

Definitely block the player and mute them. You'll be good afterwards!