Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
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When you installed your Office 2013 and entered the email address and password for a Microsoft Account this created an Office Account. You should be able to access your office account using the same email address and password at: https://www.office.com/myaccount
If you can access your Office Account this would be proof of license. If you still have problems try the help desk Microsoft Contact Us Click on>Services & Apps>Office or Office365 for Windows>Setting up>Chat