Cashless hospitalization rejected - Manipal Hospital not in network list

I have a health insurance policy from Niva Bupa with sum insured of 30 lakhs. Last week, my husband had to be admitted to Manipal Hospital in Bangalore for heart attack. When we tried to get cashless treatment, the hospital said Manipal Hospital is not in the network list of Niva Bupa. But when I bought the policy, the agent told me that Manipal Hospital is covered. Now I had to pay 2.5 lakhs from my pocket and I am trying to get reimbursement. Has anyone faced this issue? What should I do? Can I file a complaint somewhere? The TPA is also not responding properly to my calls.