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/
There, you should see your Microsoft 365 subscription.
Click the Manage button beside your subscription.
In there, you can cancel your subscription and also ensure you disable the Recurring Billing on the subscription to avoid any further subscription payments.
You may then be entitled to a refund, you can check your eligibility to a refund using the steps on this link.