See "Use iTunes to delete tones that you manually added to your iPhone ..." here:
Use tones and ringtones on your iPhone, iPad, or iPod touch - Apple Support
Apple Event: May 7th at 7 am PT
See "Use iTunes to delete tones that you manually added to your iPhone ..." here:
Use tones and ringtones on your iPhone, iPad, or iPod touch - Apple Support
See "Use iTunes to delete tones that you manually added to your iPhone ..." here:
Use tones and ringtones on your iPhone, iPad, or iPod touch - Apple Support
You might want to explore the device with iFunBox or similar and see if you can locate and delete the .m4r files from the device manually. See also Create and manage ringtones in iTunes.
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How do I remove ringtones from my phone that are not listed in ‘Tones’ in iTunes?