Room rent limit causing claim deduction - need advice

My mother was hospitalized for 7 days for cancer treatment. The total bill was 20 lakhs. My health insurance policy has a room rent limit of 3000 per day, but the hospital charged 12000 per day for the room. Because of this room rent capping, the insurance company has proportionately reduced my entire claim and only paid 3 lakhs. I had to pay 6 lakhs from my pocket. I did not know about this room rent proportionate deduction clause when I bought the policy. Is this fair? Can I challenge this? Should I upgrade my policy to remove room rent limits? Please advise.