In any proceeding, whether upon the Commission’s own motion or upon complaint, involving the rates or practices of any public service company, the Commission may exclude in whole or in part from the accounts of such public service company any payment or compensation to an affiliated interest for any services rendered or property or service furnished, as above described, under existing contracts or arrangements with such affiliated interest, if it shall appear and be established upon investigation that such payment or compensation or such contract or arrangement is not consistent with the public interest. In such proceeding any payment or compensation may be disapproved or disallowed by the Commission, in whole or in part, unless satisfactory proof is submitted to the Commission of the cost to the affiliated interest rendering the service or furnishing the property or service above described.