Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hello, good day and thanks for your question. I understand that you are looking into merging your account that has a Microsoft 365 subscription to your other Microsoft account.
If you are referring to merge like transferring your subscription from one account to the other, you will not be able to do it as the subscription is not transferrable.
The option here is to get help with the support team to check if there will be an option to cancel and an option to request for a refund and then subscribe again to Microsoft 365.
Also, you will need to change/replace the card or the payment method that you have used to avoid future charges on the account that you do not have access to anymore.
You can reach out to the support team at https://support.microsoft.com/en-us/contactus/ and then click on Microsoft 365 and then click Get Home Support and then type in Billing question and click the blue button that says Sign in to contact Support and login and proceed from there.