Why do I get messages saying storage is full when only using 14.2gb of 50gb I pay for?

This is email I keep getting & when I check on phone etc I am using 14.2 gb?

Hello Nigel L., Your iCloud storage is full. You have exceeded your storage plan and this means that your documents, contacts, mail and device data are no longer being backed up to iCloud and your photos and videos are not being uploaded to iCloud Photos. iCloud Drive and iCloud-enabled apps are not being updated across your devices. To keep on using these iCloud services, you need to upgrade your iCloud storage plan or reduce the amount of storage you are using. Upgrade to 50 GB for £0.79 a monthImportant: If you do not purchase additional storage or reduce the amount of storage you are using soon, you will not be able to send or receive messages with your iCloud email address ******@me.com. Sincerely, The iCloud Team iCloud is a service provided by Apple. 

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[Personal Information Edited by Moderator]

Try signing out of the device and back in, and if you see the same with your storage bar, consult with - Contact - Official Apple Support.

Are you certain the message is referring to your iCloud storage being full and not your device's storage being full? Can you re-check and clarify.