Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
1
If you have Office installed on a PC, open Word, then go to File - Account.
On that window, you should see the Email address of the Microsoft account used for the Office subscription.
2
If you do not have Office installed on any device, log into any Microsoft account you may have on this link to try to find the subscription, if not, click the Billing icon on the left, to try to find your Microsoft 365 subscription payment.
https://account.microsoft.com/services/
3
If you are still unable to find your subscription, this forum is just a user to user forum, no-one here has any account access, you will need to contact Microsoft Support directly and provide them with your payment details, they may be able to trace the associated account for you, 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