Unreasonable Delay from Employer for Full & Final Settlement

My previous employer where I was working as an software engineer is unreasonably delaying full and final settlement. I have served required notice period, received Experience certificate and completed all the handover formalities there is nothing due from my side. As per company policy they have hold my [Last mont salary + last quarter's bonus + Amount for Pending Paid Leaves] which is payable in 45 days from my last working day. Its more than 2 months now but I have not received any response from them. I have tried sending several reminders to HR through Telephone & Email. I have already escalated the case to company's MD through email but I have not received any response (Not even reason for delay or any assurance for settlement). Followings are my questions : 1. What should be the wait time before approaching lawyer or taking any legal actions ? 2. Is it legal on Employer's part to hold my money for 45 days or more ? 3. What should be the interest rate that can be charged to my employer for the all the days they delay ? Any help in this regards will be highly appreciated. Thanks in advance.