I'm having this problem in the non beta version of iOS 9.
Basically my iPhone 6 backed up after upgrading to iOS 9. Before the backup I had about 2.1 GB free but after the backup I only had about 132 MB of free iCloud storage out of 5 GB. Of the iCloud storage listed on my iPhone 6:
- 48 MB was for a very old iPhone
- The iPhone 6's backup was reported as 0 MB
- 2.5 MB was for documents and data, and
- 5.6 MB for e-mail.
When I looked on another phone, the iPhone 6's backup wasn't even listed.
I tried deleting the backup but I get an error messag.