Songs delete, memory doesnt

Ok, I put some songs on my MP3 and didn't want them anymore, so I deleted them. When I tried to put new ones on, it said the memory was all taken up. When I go to the playlist, it says there are no songs, but their memory space still takes up all of the memory. I never have had anything on it except the songs, so that's what is taking up the space even though i cannot find them on it.