Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Office Home & Business 2021 is a one-time payment version of Office, if that is the licence you have, you should not need to pay a subscription for the Microsoft 365 version of Office.
Log into your Microsoft account on this link.
https://account.microsoft.com/services/
Do you find both your Office Home & Business 2021 licence and a current Microsoft 365 subscription listed there?
If so, you should be able to uninstall Microsoft 365 from your PC, then download and install Office Home & Business 2021 onto your PC, and ensure that is working correctly, you should then be able to cancel the Microsoft 365 on your account online.