After September 30, 1985, or upon occurrence of a vacancy in either the office of tax assessor or tax collector, there shall be a county revenue commissioner in Cleburne County. A commissioner shall be elected at the general election in 1984 and at the general election every six years thereafter, who shall serve for a term of six years beginning on the first day of October next after his or her election, and until his or her successor is elected and has qualified.