S.C. Code Ann. § 58-11-40: Compensation different from that in schedule shall not be charged or received.

No radio common carrier shall directly or indirectly, by any device whatsoever, or in any way, charge, demand, collect or receive from any communications person or corporation a greater or less compensation for any service rendered or supplied, or to be rendered or supplied, such radio common carrier, than that prescribed in the schedules of such radio common carrier applicable thereto then filed in the manner provided in this chapter, nor shall any person or corporation receive or accept any service, from a radio common carrier for a compensation greater or less than that prescribed in such schedules.