The department may also, upon its own motion, review any decision of a regional director, or a designated agent, and county mayor, and may consider any application upon which a decision has not been made by the regional director, or a designated agent, within a reasonable time. The department may make such additional investigation as it may deem necessary, and shall make such decision on such application as in its opinion is justified and in conformity with this part. Applicants or recipients affected by such decisions of the department shall be notified of such decision in writing, and shall, upon request, be given reasonable notice and opportunity for a fair hearing by the department. All decisions of the department shall be final and shall be binding upon the county involved and shall be complied with by the regional director or a designated agent.