Today, Apple has just released the Apple’s iOS 8.1.2 update through over the air (OTA) to fix bugs, including ringtone issues: purchased ringtones were removed from devices. If your ringtones were removed, you can simply visit here to restore it.
This update is available for all of Apple’s device running iOS 8 such as iPhone 4S to iPhone 6 Plus, iPad 2 to iPad 4, iPad mini, iPad Air and iPod touch 4-th.
Have you got the OTA notification ? If not, go to Setting and let check for update.