All persons engaged in the taxicab business in the city operating under the provisions of this chapter shall render an overall service to the public desiring to use taxicabs. Holders of certificates of public convenience and necessity shall maintain a central place of business and keep the same open twenty-four hours a day for the purpose of receiving calls and dispatching cabs. They shall answer all calls received by them for services within the city as soon as they can do so and if such services cannot be rendered within a reasonable time they shall then notify the prospective passengers how long it will be before such call can be answered and give the reason therefor. Any holder who shall refuse to accept a call anywhere within the city at any time when such holder has available cabs or who shall fail or refuse to give overall service, shall be deemed a violator of this chapter and the certificate granted to such holder shall be revoked at the discretion of the city clerk. (Prior code § 22-1-5)