I don't see any backups but iCloud is full

Hello ~ Then your best option would be to contact Apple Support by going to lower left and click on Support or…

Contact Apple for support and service

Take care and should you contact them perhaps you can post the solution here?

~Katana-San~

katya287 wrote:

Could you cleanup the backup's space

No, but you can. Apparently you have iCloud backups from previous devices out there.

See “Delete backups and turn off iCloud Backup for your device“ in the article linked above.