A Microsoft file hosting and synchronization service.
Hi, first save a copy of your edited document to a folder on your Mac outside OneDrive, so your changes are safe.
Open https://onedrive.live.com and sign in with the account showing 0.7 TB free. Try uploading the saved copy under a new name to My files.
If that works, check that Word is saving to the same OneDrive account. Sign out of Word, quit it completely, then reopen it and sign back in to refresh the connection.
If the website also reports insufficient storage, please share a screenshot of that error and the online storage usage, hiding your email address.