Miscellaneous topics that do not fit into specific categories.
In your account at https://account.microsoft.com/services , turn off recurring billing if it is currently enabled, and then you should be able to cancel. See also https://support.microsoft.com/en-us/accounts-billing/subscriptions/cancel-a-microsoft-365-subscription .
The rules for refunds are discussed in the support article at https://support.microsoft.com/accounts-billing/subscriptions/how-to-get-a-refund-on-a-microsoft-subscription .