Can't downgrade iCloud+ with Apple One subscription
I have iCloud+ subscription of 50GB. I have now subscribed to Apple One subscription with 50GB of storage. The Apple One plan is currently in trial phase and I intend to continue with it post trial phase.
With both plans I now have 100GB of iCloud storage of which I am using 31GB. I want to cancel my iCloud subscription but when I try to downgrade it I get message "You are currently using more than 5GB of storage." and does not allow me to cancel it.
How can I cancel my current iCloud+ subscription and use the Apple One's iCloud subscription?