Any policy filed under the provisions of this chapter may be canceled, as to accidents occurring subsequent to the effective date of such cancellation, by the insurer or by the owner upon the terms and in the manner therein provided for; but such cancellation shall not be effective unless and until 20 days' notice in writing of such cancellation shall have been given to the City Clerk. Service of such notice of cancellation may be made either personally, or by registered or certified mail, and directed to the City Clerk at City Hall, Clifton, New Jersey. Immediately upon receipt of such notice by the City Clerk of the cancellation, as required by this chapter, or if the authority of the insurer to transact business in the State of New Jersey shall be revoked, the City Clerk shall require the owner to replace such policy with another good and sufficient policy in accordance with the provisions of this chapter, in default of which the owner's certificate shall be revoked for all motor vehicles covered by such policy, and the owner shall thereupon cease to operate, or cause or permit to be operated, any such motor vehicle. Upon revocation of the certificate of compliance of any owner by the City Clerk, other than for failure to file another policy upon notice of cancellation, as hereinabove provided for, notice shall be sent by the City Clerk to the insurer, and such notice of revocation shall operate automatically to cancel such policy for the motor vehicle for which the certificate was revoked, as to all accidents occurring subsequent to the revocation of the certificate, and such insurer shall be liable for the return of the unearned premium upon such policy, as in case of cancellation by the insurer.