The employer may change the insurance company to provide insurance coverage, under the condition that it shall forward a letter to that company by one month at least as of the date of required cancellation, and shall forward a copy of the letter to CCHI. The refundable portion of the insurance premium shall be calculated on a pro rata basis. The employer (policyholder) shall return the insurance cards on the cancellation date and signs another policy to provide insurance coverage to begin on the day following the date of cancellation of the old policy, according to the provisions of Article (9) of the executive regulations of the cooperative health insurance law.