Dear @Tom Farrell
If the subscription was purchased directly from Microsoft, sign in to the Microsoft account used for the purchase and go to Services & subscriptions. Find the subscription, select Manage --> Cancel, and follow the steps shown. During the cancellation process, Microsoft will let you know whether the subscription is eligible for a refund.
If no refund option is shown, you can also contact Microsoft Support.
https://support.microsoft.com/en-us/accounts-billing/subscriptions/how-to-get-a-refund-on-a-microsoft-subscription
If you purchased the subscription through a third party, such as Apple, Google Play, Amazon, or another retailer, you will need to request the refund from them, as Microsoft cannot refund payments that were processed by another provider.
https://support.microsoft.com/en-us/accounts-billing/subscriptions/manage-your-microsoft-365-subscription-purchased-through-a-third-party
Best regards,
Bence