Cashless hospitalization rejected - Apollo Hospital not in network list

I have a health insurance policy from Max Bupa with sum insured of 20 lakhs. Last week, my wife had to be admitted to Apollo Hospital in Chennai for severe pneumonia. When we tried to get cashless treatment, the hospital said Apollo Hospital is not in the network list of Max Bupa. But when I bought the policy, the agent told me that Apollo 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.