At the time and place designated in the notice, or at any subsequent time to which the hearing is postponed, the board of supervisors shall hear any reason that may be submitted for or against the granting of the petition. If the board of supervisors deems it for the best interest of the district named in the petition that the unsold bonds be canceled, it shall make and enter an order in its minutes that the unsold bonds are canceled. Thereafter the bonds and the vote by which they were authorized to be issued have no validity whatever.