law: 86. Notice to be given of the circumstances in which remission or refund is claimed.
  No remission or refund under section 84 or section 85 shall be made unless notice in writing of the fact that the building, land or tenement has become vacant and unproductive of rent, has been given to the Chief Executive Officer and no remission or refund shall take effect in respect of any period commencing more than fifteen days before the delivery of such notice.