The commission, whenever it shall have completed a valuation of the property of any public utility and before such valuation shall have become final, shall give notice by registered or certified mail to such public utility. If, within thirty days after such notice, no protest shall have been filed with the commission, then said valuation shall become final. If notice of protest shall have been filed by such public utility, the commission shall fix the time of hearing the same and shall consider at such hearing any matter material thereto presented by such public utility in support of its protest. If, after the hearing of any protest, the commission shall be of the opinion that its inventory is incomplete or incorrect or that its valuation is incorrect, it shall make such changes as may be necessary and shall issue an order making such corrected valuation final. The final valuation by the commission and all classifications made for the ascertainment of such valuations shall be public and shall be prima facie evidence relative to the value of the property.