unable to access memory frombefore update

I had a large number of talking books stored on my iPhone 5 . I used it continually. when I updated the phone there seemed no problem - I could still listen to the books, but when I tried to update my books through the iTunes on the computer, it could not delete or overwrite the old books - we had a similar problem with OS 7 and learnt to delete them from the phone individually - a pain but do able. tried the same thing the phone tells me I have 45 gb used on the phone but when I enter usage to delete nothing shows up. I have 'added' 7 new books, filling my storage and they appear on phone, the old ones don't. I cant listen to them , cant see them, cant delete them - I am contemplating a complete delete and reinstall of the phone. frustrating to say the lest.