Hidden mp3 file

So I downloaded this soundboard app on my phone then later on deleted it. But I realized when I was in playlist in Play Music that the mp3 files for the soundboard was still there. I want to delete them but theres hundreds so it will take me awhile. I also can't find it on Download app. It bugs me so much because when i want to find the music I want to listen to, I have scroll down hundreds of the soundboard files before reaching what I want.

Welcome to Android Central! Did you install it from the Play Store, or from some other source?

Use a file manager app to look through the various directories on the phone, and see if you can find the directory with all of those mp3 files. Sometimes uninstalling an app won't completely get rid of all of its associated data directories.