(a) This chapter does not restrict:
(1) a consumer's right to complain to the commission about the application of an ambiguous tariff; or
(2) the commission's right to determine:
(A) the proper application of that tariff; or
(B) the proper rate if that tariff does not apply.
(b) This section does not permit the commission to:
(1) lower a tariff rate except as specifically provided by this title;
(2) change the commission's interpretation of a tariff; or
(3) extend the application of a tariff to a new class of customers.