i have installed a mp3 file on the phone and moved it to the ringtone folder (internal) and it works for a day or so then it reverts back original default tone.
I have done the fowlling:
-Reset the phone (no help at all, I have even tried it on a formated phone(s20 5G)the same issue)
-Change back from darkmode to daymode (some forums say ti would work)
-moved the file to SD-card and back