Tata Aig dispute in assessment

I am a policy holder in tata aig motor insurance . I have a bmw car 5 series where recently I met with an accident and gave my car for repair in bmw service station. The total bill amount of my car repair is 3 lacs but the tata aig have only approved 0000 thousand of the total bill . The reason is that this company has hired an external surveyor who has no idea about the high end car n have no mannner to speak with the valuable client, so on his inspection the company has only approved 30% of the total bill of repair and the 70% is ask to pay by us. The problem is why will I get my car insured with such reputed company like tata aig when they cant even assure a small amount claim. My complaint is that my car was lying in the service station for 45 days , they have ignored the urgency of repair and on top of that I had to speak n fight with the some cheap hired external surveyor to get my car claim approved as soon as possible, and now after all this I get only rs 0000 approved by him. I think this company is at stake of his reputation. Plz suggest me what to do?