Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Log into your Microsoft account on this link.
https://account.microsoft.com/services/
You should find the Microsoft 365 subscription listed, click Manage beside the subscription.
From there, you can cancel the subscription and also ensure you disable the recurring billing on the subscription.
You may then be entitled to a pro-rata refund for your latest subscription payment, you can check your eligibility to a refund using the steps provided on this link.