If a vendor is unable to collect an account receivable for which the tax already has been remitted and the vendor has charged off that account as worthless, the vendor may deduct the amount of the tax from its monthly remittance, subject to the requirements of this subsection. The vendor must:before availing itself of this privilege, provide the Director with a written statement of its policies governing the determination of worthless accounts; and as a condition of taking any deduction:keep records of every worthless account for which the vendor has taken a deduction; and make those records available to the Director, on request, for review or collection efforts. Whenever a tax imposed under this Part 2 has been erroneously, illegally, or unconstitutionally paid, the Director shall refund the tax if the application for refund:is made within 3 years from the payment of the tax; and states a proper ground for refund. City Code, 1976/83, art. 28, §56A(g)(1), (2) Ord. 99-441