Accidentally clicked upgrade iCloud storage, how do I undo so I'm not charged
This morning I got an notification that I didn't have sufficient storage for my iCloud back up. The notification gives you the option to click ok, cancel or upgrade iCloud storage. I accidentally clicked upgrade and I'm trying to 'cancel' this so that I'm not charged. Does anyone know how to do this? Please help, asap.
Thanks!
iPhone 6, iOS 9.1