iCloud says that backups are using 3 GB of space, but there are no backups
It appears you are looking at the iCloud info in System Preferences on an Apple laptop or desktop. Inside System Preferences, after you click on iCloud, you then click on Manage in the lower right corner. When that window comes up, the top option is highlighted but not necessarily selected. If it's not selected, the backups will not show in the right column. Click on Backups to make sure it is selected.

I also would recommend signing into www.iCloud.com and verifying that you have no backups in the cloud. As many of these devices back up on their own, it seems unlikely that you would have no backups unless you recently deleted them.