To be 100% I don't know an app that would do what you're looking for off the top of my head. What type of files did they save as? Can you see the full file name? Out of curiosity, have you tried connecting your phone to a laptop or desktop and seeing if you're able to view the files or modify the file names there? I'm glad you found an app you like, but it's definitely not cool if you can't listen to the songs!
Hi again - just wanted to check back in and see if you'd been able to work this out and get the files converted through another app or program! How did everything go?