Whenever a municipality pursuant to § 8-11-2 of the Illinois Municipal Code, as heretofore and hereafter amended, imposes a tax on any public utility, such utility may charge its customers, other than customers who are certified business enterprises under paragraph (e) of § 8-11-2 of the Illinois Municipal Code or are exempted from those taxes under paragraph (f) of that Section, to the extent of such exemption and during the period in which such exemption is in effect, in addition to any rate authorized by this Act, an additional charge equal to the sum of (1) an amount equal to such municipal tax, or any part thereof (2) 3% of such tax, or any part thereof, as the case may be, to cover costs of accounting, and (3) an amount equal to the increase in taxes and other payments to governmental bodies resulting from the amount of such additional charge. Such utility shall file with the Commission a true and correct copy of the municipal ordinance imposing such tax; and also shall file with the Commission a supplemental schedule applicable to such municipality which shall specify such additional charge and which shall become effective upon filing without further notice. Such additional charge shall be shown separately on the utility bill to each customer. The Commission shall have power to investigate whether or not such supplemental schedule correctly specifies such additional charge, but shall have no power to suspend such supplemental schedule. If the Commission finds, after a hearing, that such supplemental schedule does not correctly specify such additional charge, it shall by order require a refund to the appropriate customers of the excess, if any, with interest, in such manner as it shall deem just and reasonable, and in and by such order shall require the utility to file an amended supplemental schedule corresponding to the finding and order of the Commission.