Reverting back to older version from Windows 10

I have the Verizon version of the phone.

I am having so much trouble reverting back from 39A to 27A through KDZ method. I've tried TOT method as well, but it isn't working under Windows 10.

I do not have learning disability. So, I have followed all the instructions on how to use KDZ and TOT.

Any advice?

why is my ringtone reverting to the default?

This is a strange one.
I have uploaded some songs onto my phone's memory (not SD card) and set one of them to be my ringtone for all contacts.
It works OK for a while, and then suddenly when someone calls me, I hear the default ringtone of the device (instead of the one I set)...
Then, when I go to the device's Sound & Notifications settings, I see that the ringtone that's displayed as the selected one is still the one I manually selected, but when i try to play it, it plays the default phone ringtone instead.
I can only get the real song to play after i remove it from the list and re-add it.

Any ideas?
I already turned the Ringtone ID setting off, and I have no SD card installed on the device.