Backup uses iCloud space although disabled

Hi all,

here's my problem:

I own a iPhone 5 64GB IOS 9.

Although Backup is disabled in my iCloud setup, 700MB of iCloud storage look assigned to Backup in both icloud.com and iCloud for Win control panels.

Through the ARCHIVE button on iCloud for Win control panel, I wanted to delete the Backup but the detail window is empty and I have no chance to delete it.

I also tried to logout from iCloud and to re-login but no way.

Finally I tried to enable Backup on iCloud (to disable it after one full cycle) but I had no success since its size looks too big.

Any advice on how to delete this backup?

Thank you in advance

Riccardo