I purchased 20 G last year and you are saying I have used it up!! I don't think so!! You need to correct your records!! I am not paying you anything else because I haven't used but half my storage space!!!!
Are you using the same email address for Photoshop.com as you are using for this web site? If so, I see that you have used only half of you total capacity, so you should not be getting an error about being out of space.
Are you getting the error from Photoshop Elements Organizer? If so, have you verified that you have the correct email address for your log in? Can you try logging out and logging back in again to make sure? Can you post a screen shot of Preferences > Backup and Synchronization?