iCloud storage reporting backups that do not exists
If you have two iOS devices, I would compare the Settings - iCloud - Storage - Manage Storage screens to ensure both agree. One device can get stale or cached data. If you don't have two, restart your device to check that it's updated.

If so, you will then want to go to iCloud.com on a computer and verify the number there. The web app allows you to clean or observe the rest of the backups. They are deleted photo albums (potentially) as well as backups of calendar, contacts, files and bookmarks.

IF at that point, you still think there's something missing - you'll want to escalate to Apple Support to http://apple.com/support/icloud