Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
There is no method provided to merge subscriptions on two different Microsoft accounts, this forum is just a user to user forum, no-one here has any account access, try using the steps they provide on this link to find out what the second payment is for.
Then use the steps they provide on this link to cancel the second subscription/payment and get a refund.
2
If you are still unable to resolve that second payment problem, you will need to contact Microsoft Support directly, try using this method to contact their support.
Go to this link: https://support.microsoft.com/contactus
Select Microsoft 365
Click 'Get Home Support'.
In the box provided, type billing.
Press Enter, then on the next page, scroll down and click 'Sign in to Contact Support'.
Navigate to Microsoft 365 and Office - Manage my Subscription.
Select the 'Chat with support agent in web browser' option