Cashless hospitalization rejected - Narayana Health not in network list

I have a health insurance policy from Star Health with sum insured of 5 lakhs. Last week, my sister had to be admitted to Narayana Health in Delhi for heart attack. When we tried to get cashless treatment, the hospital said Narayana Health is not in the network list of Star Health. But when I bought the policy, the agent told me that Narayana Health is covered. Now I had to pay 4 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.