Storage is still in use for iCloud Photo library

I have following all the instructions in trying to delete the photos on my iPhone 6, but my phone still shows that over 5.5GB of storage is in use for photos. However I have turned off iCloud photo sharing, I've deleted all my photos and attempted to follow the instructions to delete the shared photo library on iCloud, but when I go to Settings>Storage>Manage Storage to delete the Shared Photos, no share photo library is on the list. However it's still using 5.5 GB for these photos that aren't actually on my phone! When you go to Photos, there are no photos, no share photos and no albums. I have synced with my desktop and set it up to not download any photos to my iPhone,but still, 5.5GB is in use. How do I free up this storage???