If someone asks them to do so, it would be disresepctful to do otherwise. Remember, in the olden days, no one had last names. Tehy were known by their first names, i.e. Mottel the Tailor. Hillel. One might preface that name with Rav, or Reb, but the first name was the only name in msot cases. So it was not disrespectful l’chatchilah. I have always preferred to be called by my given name. the only exception is when I first meet the younger person, and I want to see if his or her middos are sufficiently respectful in other areas. If not,then I remain Mrs. ______ to them. I have yet to be disappointed.