If any transfer of any such mortgage, deed of trust, contract of conditional sale, or other instrument of like character described in Section 40-22-6 has heretofore been filed for record in any probate office of this state and the recording privilege tax imposed by Section 40-22-1 or Section 40-22-2 has been paid thereon, the debt secured by the instrument so transferred shall be exempt from any ad valorem tax, either state, county, or municipal.