If you subscribed to STARZ through Microsoft on Xbox One, this page explains how to cancel your subscription:
From a computer:
- Go to https://account.microsoft.com and sign in.
- Find the STARZ subscription and select Manage.
- Then Change and Turn off auto-renew.
- Select Confirm Cancellation.
When you cancel your subscription, you will still have access to STARZ until the end of that billing cycle.
If you have any questions, please contact Microsoft at https://support.microsoft.com or 1-800-469-9269.