A surprising number of younger people are actually on board with the Title + Surname format in this area. Adults usually ask if I’d prefer their children refer to me as Ms. Firstname or Ms. Surname.
My surname is as much my name as my first name. I don’t know why you find that concept alien.
I find the “Southern custom” to be offensive.
^ Very much this.
I am happy that the medical providers in this area default to Title + Surname. It is demeaning if I have to address doctors and nurses by their surname but they call me by my first name. That’s infantalizing.