N.D. Cent. Code § 49-06-09

If the final rates fixed, determined, and prescribed are less than the temporary rates fixed under the provisions of section 49-06-07, the public utility shall pay or remit to each of the several customers, patrons, or users such sum as such customer, patron, or user has paid to the said utility for the said service over and above the amounts that would have been paid during such time had the rates fixed, determined, and prescribed in the final order been in effect during the period that the temporary rates were in effect.