Welcome to iMore! Many people are having this issue. It's an iOS 8 bug. Apple is aware of it and is working on a fix. For now, you might call or email iTunes. In the future, be sure to sync purchased ringtones to iTunes on your computer. Ringtones and audio books are not put in a purchased list. You can only download them once. So as soon as you purchase a ringtone, sync it to iTunes in a tones section. I'm not sure about that. But that's what I read. It goes somewhere in iTunes where it stays safe. Good luck.