I turned off iCloud backups - but I am still using 800 MB

My iPhone and iPad photo collections were running up against the 5 GB storage limit in iCloud.

So I turned off iCloud backups on my iPhone, iPad, iPod touch (all with iOS 9), with the plan of trimming the photo collections and other miscellaneous items included in backups, and then turning back on the backups.

With all backups deleted, and no new ones created, iCloud says I am using 800 MB of storage. A

nd I don't use iCloud drive, so my various apps should be using < 10 MB. N

one of the iOS devices seem to have a way to free that 800 MB.

And iCloud in my Mac Safari login shows that usage, too.

On my Mac, I tried System Preferences > iCloud > manage (which should let you delete unwanted backups).

The Backups category also shows the 800 MB used, but no devices or backups are listed, so I cannot use the Delete option.

How do I get rid of the 800 MB of storage usage?