D.C. Code § 47-2007
No administrative or civil action for the collection by the District of Columbia from a vendor of taxes (or penalties and interest thereon) due and payable on sales made prior to January 1, 1978, which would have been exempt sales under § 47-2005(19) if such sales had been made on or after January 1, 1978, shall be commenced after the effective date of this section. Any such administrative or civil action that was commenced on or after January 1, 1978, shall be terminated, and any taxes, penalties, and interest collected from a vendor pursuant to any such administrative or civil action commenced on or after January 1, 1978, shall be refunded in accordance with § 47-2020, notwithstanding the limitation in such section on refunds of taxes finally determined as due under § 47-2019; provided, that no interest shall be allowed or paid on any amount refunded pursuant to this section.
D.C. Code § 47-2007