How can I stop someone from bullying me?

You don't contact a department.

You can stop that person yourself. Bring up the profile that is bullying you on your console, and then Block and Mute that profile. That will prevent the person from messaging you and to be heard by you in online chats.

However, be aware that as soon as you message that person yourself (e.g. you feel the need to tell him you blocked him now), you will automatically un-block the person again!!!

So do NOT reply to the person bullying you, and just mute and block him.

If the person bullying you is using multiple accounts to get around your blocks, go to
https://account.xbox.com/settings and temporarily set your online and privacy settings to "Friends only". That way, only people that are on your friend list can message and talk
to you.

If you already received bullying and threatening messages, use the reporting feature on your console to report these messages.

This will then send a report with the message attached as proof to the Xbox Live Policy Enforcement Team, who will then review your report.

If the attached message violates the Xbox Live Code of Conduct, they can then issue suspensions or bans for this person.

If you think someone is harassing you online just report that person or block him to avoid further abuse.

I don't recommend this in the slightest. Although that may have been the past, Xbox has always been aiming to change their community to be more friendly. Please keep this in mind.

As others posted above, blocking, reporting, and not messaging them back afterwards is the route to go!

You can block but if you don't want to you can report them and if there bullying you and sending you messages then report their message

Let me give you some personal advice.

Most people are bullied because they are better than the people who bully them.

Anyways.

Xbox has an ingame option to block players and communications they have with you. Where they can no longer contact you. Hope this helps! Keep your head up and don’t ever let someone get to you.