Medical claim delay from the insurance company how to file suit

Hi I have applied for mediclaim reimbursement for my mother after surgery with Vipul mediclaim after submitting the Hospital docs and the Physical verification in the Hospital by Vipul team was also over. As per their norms they say 10 - 15 days for reimbursement but it is more than 60 days now but every time when I reach then they ask for a query and once I submit they say that it is in Process like this I have waited enough. Now I have lost my patience and wanted to issue legal notice. This is applied through our corporate agency of our organization. Please let me know what should I do from now. The claim amount is 3 Lkahs.