I have been trying to remove several custom ringtones from my iPhone 6S Plus for 6 months or more, without success. I have called support many times and they tell me they know about the problem and are working on a fix. They have had several software iterations, but no fix yet. I was successful removing them on my Mac in iTunes, but they are not removed from the phone. I've removed ringtone apps and that did not remove them. I have an alarm app that uses them, but I don't think that's the problem. Does anyone have an answer for this?