Every policy of industrial sick benefit insurance issued in this Commonwealth after June 18, 1922, shall contain a provision that:
1. The sick benefit portion of the policy may be cancelled by either the insurer or the insured and the life portion continued by a payment of twenty percent of the original premium;
2. If the cancellation is by the insurer, it shall be without prejudice to any claim arising on account of disability commencing prior to the date on which the cancellation takes effect; and
3. Written notice of the cancellation and payment for the unearned portion of the premium shall be delivered to the insured or mailed to him at his last known address.