Unsub from Gamepass

Navigate to account.microsoft.com/services.
Sign into your Microsoft account.
Navigate to the Xbox Game Pass subsection of the page.
Click Manage.
Choose Turn off auto-renew.
Select Confirm cancellation.

Hi there,

You can stop your auto-renewal by using this link http://account.microsoft.com

If you already been charged and you don't want the subscription, I suggest to contact the official Xbox support about this by using this link support.xbox.com/contact-us

Thank you!

Also keep in mind that if you agreed to a promotion you may still be billed once depending what the terms are.

Please go here
https://account.microsoft.com/services/ And beside Xbox Game Pass, click "cancel automatic renewal."

The basics of it are

Gold games that you already have are only yours while subbed and become unplayable if unsubbed, 360 games that were given with gold are yours to keep forever.

gamepass core, all previous games with gold games apart from 360 games are yours while subbed and become unplayable when unsubbed, games provided by gamepass core are only playable while they are available and while you are subbed.