Payments received by a public utility without written instructions that they be applied to merchandise, appliances, special services, meter testing fees or other nonbasic charges and which are insufficient to pay the balance due for the items plus amounts billed for basic public utility service shall first be applied to the basic charges for residential public utility service.
52 Pa. Code § 56.23
The provisions of this §56.23 amended under the Public Utility Code, 66 Pa.C.S. § § 331, 501, 504, 1301, 1305, 1401-1419, 1501, 1504 and 1509.