Did you try backing up your phone after you change it? Or see if there’s an update your phone needs to do? the voice you’re choosing possibly be one that isn’t an option anymore if there is an update?
Or depending how old your phone is, maybe it’s a voice ur phone isn’t compatible with? Im sorry that I don’t have an answer & just kinda throwing spaghetti @ the wall & seeing if some sticks…
Other than turning the phone off and back on again, I would do a back up now after changing the voice.
Hope something worked for you, would love an update!