iCloud backup eating up storage
I am trying to decrease my storage on my iCloud by removing my old phones from backup. I go to settings, iCloud, Storage and then back-up. I thin click on the old phones that I want to remove, click on delete back-up, click turn-off & delete, and am then told that I cannot delete backup.
Any idea how this can be done as it is eating up lots of storage in iCloud
iPhone 6s Plus, iOS 13