No assessment shall be increased if the holder of title to land affected is known except after personal notice or notice by registered mail given to the holder of title by depositing the notice at least two weeks before the hearing in the postoffice at the place in which the office of the district is located, in a sealed postpaid envelope addressed to each of the holders of title at his last known place of residence or business. If the last known place of residence or business of the holder of title is unknown, the notice may be sent to the county seat of the county in which any portion of his land is situated. If the holder of title is unknown, the notice may be given by
publication at least once a week for two successive weeks in the county in which his assessed land is located. No assessment shall be increased except upon a hearing of objections made.