If any public utility or railroad corporation subject to the provisions of this act claims the assessment made against it is erroneous, excessive, unlawful or invalid, it shall on or before the time specified for payment of the first installment of the assessment made against it, file with the commission its written objections to such assessment, setting out specifically the grounds upon which it claims said assessment to be erroneous, excessive, unlawful or invalid. The commission, upon receipt of any such objection, and after ten (10) days’ notice in writing to the objector, shall proceed to hold a hearing upon such objections within twenty (20) days after the date of such notice. Within twenty (20) days after such hearing, the commission shall make and enter its findings in its minutes and issue its order in accordance with said findings and forthwith transmit the same to the objector by registered mail. The commission shall refund any overpayment of any fees prescribed by this act and all claims for such refunds against the "Public Utilities Commission Fund" created by this act, shall be examined by the commission and certified by the president of the commission to the state controller, who shall, upon the approval of the board of examiners, draw his warrant against said "Public Utilities Commission Fund" for all such claims for refunds so allowed and approved.