S.C. Code Ann. § 15-3-590

(1) Actions at law for the recovery of overcharges against motor carriers subject to Chapter 23 of Title 58 shall be commenced within two years from the time the cause of action accrues and not thereafter, subject to the provisions of subsection (2) of this section; provided, that if a claim for the overcharge has been presented in writing to the carrier within the two-year period of limitation, the period shall be extended to include six months from the time notice in writing was given by the carrier to the claimant of disallowance of the claim, or any part or parts thereof. (2) The cause of action against a motor carrier for overcharges shall for the purpose of this section be deemed to accrue at the time the charges are paid to the carrier. (3) The term "overcharges" as used in this section shall be deemed to mean charges for transportation services in excess of those applicable thereto under the tariffs lawfully on file with the Public Service Commission.