Dear Ashish Jain,
At the outset, let me clarify that this site is designed by a group of senior Banking Professionals to assist Bank Customers at large to provide guidance for resolution of any complain/query/grievance in respect of financial services. This site does not belong to any Bank or a regulator, which may please be noted.
It appears that you have become a victim of identity theft fraud. It is probable that some one accessed your account using your personal information like customer ID, login and transaction password etc which you might have unintentionally compromised responding to fake email purportedly from your bank and without verifying authenticity of the source. The other possibility is that your mobile number would have been got changed by an unknown person submitting application to your bank under forged signature. The fact you did not receive SMS alert or One Time Pass Code (2nd factor authentication) on your registered mobile indicates that your mobile number was got changed without your knowledge/authority.
Without wasting further time, please visit your home branch and lodge a complaint stating that the withdrawal/s in question were unauthorised. Request the bank to investigate and restore the amount. Meanwhile don't operate the account. Rather get is blocked for further operations. If your mobile number has been changed you can demand a copy of the application basis which the bank changed the number. If the number has not been changed it may indicate someone had obtained duplicate SIM. In this case you can demand the application copy from the telecom service provider
You may update your passbook or obtain a statement of account to peruse the transactions to identify the genuine and fraudulent ones before lodging your claim. If the bank's investigation reveals that you have compromised your personal information due to which the fraud had happened, the bank may disown any liability.
Be honest and factual about your claims. In case you not receive proper response from the branch you may take up with Nodal Officer of the bank whose contact details can be found on the bank's website. If your claim is genuine and the bank refuses to settle the same within 30 days of your first complaint then you may approach the Banking Ombudsman for resolution of your grievance.
While writing to the BO, please provide complete details and also enclose the communications exchanged with the bank. For address of the Office of the Banking Ombudsman, Area of Operation (jurisdiction) and the procedure for lodging complaint, you may access the website https://bankingombudsman.rbi.org.in/
Regards
J R Mohandas