How To fix Your Iphone 5C Storage Issues
Then you will have to try this. it works on 9/10 tries.
Log out of itunes store in settings, wait 10 minutes, then log back in. your storage should go back to what it should have been all along. there is an itunes media caching bug / storage leak in ios 8 (all versions so far), and apple for some reason has decided it isn’t worth fixing.