(a) If, after hearing, the commission finds the rates are unreasonable or in violation of law, the commission shall:
(1) enter an order establishing the rates the utility shall charge or apply for the service in question; and
(2) serve a copy of the order on the utility.
(b) The rates established in the order shall be observed thereafter until changed as provided by this title.
(c) This section does not apply to a company electing under Chapter 58 or 59 except as otherwise provided by those chapters or by Chapter 60.