Legal Notice from Employer. What should we do ?

Hello Sir/Madam, I Joined a Private Company as a Accounting Associates accept the offer letter through Email and not Signed the Agreement Which Says that company can terminate any time and Employee needs to give 3 months notice period or 2 Month Salary need to be paid back as a training cost before leaving. In case employee does not serve notice period there is nothing mentioned . I had to quit Company after Six month due to Not Increasing Salary and extreme stress because of worst Management. I informed HR over mail about . Since then I could reply to HR and Manager of their Calls, But Could not to MD of Company. Now they have sent a legal notice over mail saying I will left the office without prior notice and original data of Client (All the Documents are Received or Sent through Official mail in Company) we need to pay Compensate loss of Company Reputation Rs. 250000, and Rs.620000 for failure to deliver of assigned work in time and Rs.1000000 for Stealing of Documents of Clients. and paid also Rs.30000 for Cost of Training. Can you suggest what should we do?