Hi David
From what I can see, something is taking up storage space in your personal Microsoft account.
1. Remember that once you delete files from OneDrive, it goes to the Recycle bin and will remain there for 30 days, still taking up storage space. Make sure that your Recycle bin is empty (on the web).
2. You may use some Apps like the Microsoft launcher that backs up to OneDrive.
3. You may have your computer set to backup your Desktop, Documents, Pictures, Music, and Videos to OneDrive. Make sure this is off in OneDrive settings. (I think this is the problem).
4. Deleting files from the Recycle bin will take a few hours to show the correct storage allocation on the Desktop and web apps.
Let me know what you find.
Regards
Casper