S.C. Code Regs. § § 103-623
If it is found that a telephone utility has directly or indirectly, by any devise whatsoever, demanded, charged, collected or received from any customer a greater or lesser compensation for any service rendered or to be rendered by such telephone utility than that prescribed in the schedules of such telephone utility applicable thereto then filed in the manner provided in Title 58 of the South Carolina Code of Laws, or if it is found that any customer has received or accepted any service from a telephone utility for a compensation greater or lesser than prescribed in such schedules; or if, for any reason, billing error has resulted in a greater or lesser charge than that incurred by the customer for the actual service rendered, then the method of adjustment for such overcharge or undercharge shall be as provided by the following:
S.C. Code Regs. § 103-623