Refunds.

(a) Any tax that has been erroneously or illegally collected shall be refunded if application under oath is filed with the Mayor for such refund within 3 years from the payment thereof. For like cause and within the same period a refund may be made upon the certificates of the Mayor and the Collector. Whenever a refund is made upon the certificates of the Mayor and the Collector, the Mayor and Collector shall state their reasons therefor in writing. Such application may be made by the person upon whom such tax was imposed and who has actually paid the tax. When an application is made by a vendor who has collected reimbursement of such tax, no actual refund of monies shall be made to such vendor, until he shall first establish to the satisfaction of the Mayor, under such regulations as the Mayor may prescribe, that the vendor has repaid to the purchaser the amount for which the application for refund is made. In lieu of any refund required to be made, a credit may be allowed therefor on payment due from the applicant.