If it should appear that an amount of sur­charge has been paid which was not due under the pro­vi­sions of this Arti­cle, whether as a result of a mis­take of fact or an error of law, then such amount shall be cred­it against any sur­charge due, or to become due, under this Arti­cle from the telecom­mu­ni­ca­tion car­ri­er who made the erro­neous payment.

(See 750 ILCS Sec. 15.3)