It is possible you have tracks uploaded in other sections as well. Please check the following sections to see if you reached your upload limit for your account. If so, this could be why you cannot create new tracks. Any tracks in your Active, Future Releases, and Drafts sections count towards your limit and you will need to edit or delete those tracks.
IMPORTANT: To delete tracks in these sections in order to upload new tracks, please see the following help article here: How do I delete a track