iCloud Storage Downgrade unavailable for selection
I am attempting to change my iCloud storage plan from 50GB to 5GB.
I've followed the on-lne help and have reached the window that presents the downgrade option of 5GB but will not let me select it. A screen cap for my MacBook is attached.
Note how "Done" is greyed-out.
I have also attempted to downgrade via my iPhone (for the same iCloud account) and the "Done" in the top right corner of the analogous screen is similarly greyed-out.
The only possible action is "Cancel". I have checked a day or two later and this window reports that my "Current Plan" remains 50GB.
MacBook Air, OS X Yosemite (10.10.3), AirPort Time Capsule