Backup using up 3.5 GB of iCloud storage, but can’t be deleted
I keep getting alerts about my 5 GB of iCloud storage being almost full, despite me barely having used my iPad. I have disabled iCloud storage for every app I have, and disabled iCloud backup altogether. Despite this, Settings > Manage Storage shows that "Backups" is using 3.5 GB of storage. When I click on Backups, however, the next page says that there are No Backups, and 0 kB of Documents and Data.
How can I clear this 3.5 GB of wasted storage?