I've been banned for a week for messaging but no details were included

I have and its been denied

If it was denied then nothing else can be done except waiting out the suspension.

If it gives you the option to submit a case review, you'll want to do so. Sometimes with that, they will give more information.

I have and its been denied

Bans are not handed out instantly, it could have been weeks ago... so this message mat not have been why you were banned.

No one here can offer any insight as Tis why you were banned, check the enforcement website
enforcement.xbox.com

You can apply for a case review if your ban is longer than 24 hrs. https://enforcement.xbox.com/en-US/home/howto#sub-topic0-6 Also, this ban could
have been from something you done a day, a week, or 2 week ago. In the message you recieved it should tell you why you was ban. And onece you go the enforcement site you can review more detail about your ban. For example, if you got ban for sending an inapprociate
message it will show the message you sent. Best of luck!