What is the ruling on the amount that was reduced from the surgical operation's bill in exchange for cash payment, given that the insurance paid the full amount based on the original bill?

It is permissible to license commercial health insurance out of necessity. If the patient pays a portion of the health insurance bill and receives a discount for immediate payment, he must inform the insurance company of this and take only what he has paid from them. He may divide the discount proportionally between what is his due and what is the company's due. If the company's system does not allow for a refund after being informed of the truth, then there is no blame on him for taking the full amount.