Any provision in any health service contract issued by a health service corporation denying the insured or subscriber, subscriber member, officer, or employee, in case of accident or sickness, the right to consult or employ any doctor, including doctors of chiropractic, licensed to practice in this state whom the insured, subscriber, subscriber member, officer, or employee may choose, or to enter any hospital or sanitarium organized and operating under the laws of this state which the insured, subscriber, subscriber member, officer, or employee may select, is void. The health service corporation must recognize any proof of claim duly certified by the doctor, hospital, or sanitarium notwithstanding any provision contained in the contract.