Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Log into your Microsoft account online on this link:
https://account.microsoft.com/services/
On that link, you should see the Microsoft 365 subscription, select that and click the Manage button.
In there, you can cancel the subscription and also, while there, disable the recurring billing on the subscription.
You should then be entitled to a pro-rata refund within 5 business days, you can check your eligibility to a refund using the steps on this link.