Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Log into any Microsoft account you may have on this link.
https://account.microsoft.com/services/
Do you find your Microsoft 365 subscription listed on your account?
If so, click the Cancel subscription on the Microsoft 365 subscription, then confirm the cancellation.
You should also remove the recurring billing on the subscription to ensure no more payments are taken from your account.
On this link, you can check your eligibility for a refund after cancelling the subscription.
If you are unable to find the Microsoft 365 subscription on your Microsoft account online, using any Microsoft account you may have, try using the steps they provide on this link to find out what that payment is for.