N.C. Gen. Stat. § 62-132
The rates established under this Chapter by the Commission shall be deemed just and reasonable, and any rate charged by any public utility different from those so established shall be deemed unjust and unreasonable. Provided, however, that upon petition filed by any interested person, and a hearing thereon, if the Commission shall find the rates or charges collected to be other than the rates established by the Commission, and to be unjust, unreasonable, discriminatory or preferential, the Commission may enter an order awarding such petitioner and all other persons in the same class a sum equal to the difference between such unjust, unreasonable, discriminatory or preferential rates or charges and the rates or charges found by the Commission to be just and reasonable, nondiscriminatory and nonpreferential, to the extent that such rates or charges were collected within two years prior to the filing of such petition.
N.C. Gen. Stat. § 62-132