No general obligation refunding bonds shall be issued pursuant to s. 132.35 unless the chief financial officer of the unit, or such other official as may be designated by the governing body, shall have first filed with the governing body of the unit a certificate, which shall be final and conclusive upon all parties:
(1) Setting forth the present value of the total debt service savings which will result from the issuance of the general obligation refunding bonds computed in accordance with the provisions of s. 132.35; and
(2) Demonstrating mathematically that the general obligation refunding bonds are issued at a lower net average interest cost rate than the net average interest cost rate borne by the general obligation bonds to be refunded.