It shall be the duty of every seller, in acting as the tax collecting medium or agency for the city, to collect from each purchaser for the use of this city the tax hereby imposed and levied at the time of collecting the purchase price charged for its public utility service; and the amount of tax actually collected during each calendar month shall be reported by each seller to the City Treasurer and each seller shall remit the amount of tax shown by such report to have been collected to the City Treasurer on or before the last day of the second calendar month following the month in which collected, together with the name and address of any purchaser who has failed or refused to pay the tax so imposed and levied by this article. The required reports shall be in the form prescribed by the City Treasurer.