Audio disappeared

I added an audio file and I didn’t like it so I deleted (at least it disappeared). When I went to add a new audio file, It wouldn’t let me add it to the tope audio track but I could add it to the one below. When I previewed it, the correct audio file played, but when I went to save it as a custom, it said that I had a copyright file (which was the one I deleted) and it would not copy it. It said that part of the slideshow would be missing music. This deleted file also shows up in the credits. How do I get rid of an audio file that I cannot see?