Ask HDFC ergo to furnish copy of govt notification that lays down cap for hospital charges
2) complain to IRDA against HDFC ergo failing to pay your hospital expenses
3) complain to state govt against exhorbitant bills charged by private hospital and to direct hospital to refund excess amount charged
4) if necessary file complaint against hospital and insurance company before consumer forum and seek orders to direct hospital to refund excess charges . In alternative to direct insurance company to pay hospital charges