Not less than ten days in advance the Commissioner shall give notice of the time and place of the hearing stating the matters to be considered at the hearing. If the persons to be given notice are not specified in the provision pursuant to which the hearing is held, the Commissioner shall give notice to all persons directly affected by such hearing. In the event all persons directly affected are unknown, notice may be perfected by publication in a newspaper of general circulation in this state at least ten days prior to the hearing.