Missing iCloud Storage

The past few days I had been getting a notification on my iPad 2 and iPhone 6 Plus that iCloud didn't have enough storage space to perform a backup. I went into iCloud from my Windows PC and went through and deleted everything under "Backups" and "Documents and Data." However, it still says 2.5 GB are being used in the "Backups" group with nothing listed. Is there anyway to reclaim this half of my storage space?