Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
If you have two separate Microsoft 365 subscriptions on two accounts, before proceeding to cancel one of the subscriptions, you will loose the OneDrive online storage that comes with the subscription you want to delete and the OneDrive storage on that account will revert to 5GB on that account, so you need to log into OneDrive online (https://onedrive.live.com/) on that account to download any files that may be stored on OneDrive on that account to ensure you have a safe copy of the files on your PC, you will not loose your Email data provided your storage does not exceed the 5GB of OneDrive storage on that account.
To cancel the Microsoft 365 Classic subscription, log into that account on this link (https://account.microsoft.com/services/), click Manage beside the subscription, from there, you can cancel the subscription and also ensure you disable the recurring billing on the subscription.