Mr.Arvind
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 is unfortunate that someone had accessed your account and transferred funds. I presume that you have not compromised your internet banking credentials responding to any phishing emails/calls?. If my assumption is wrong then you will have to take responsibility for the fraud. As the internet banking credentials are the key to access to your account and any compromise of such personal information, knowingly or unknowingly will not be accepted by the bank. In such a situation, though you have become a victim, as one who had compromised, you have to bear accountability for the fraud.
On the other hand, if you are emphatic that you never compromised any personal information leading to depletion of funds in your account, you can and should hold the bank accountable. I suppose all the transactions would have gone through multiple authentication process including One Time Password (OTP). The OTP would have been communicated on your mobile number registered with the bank. Please check if you have received the OTPs for each and every transaction. Since you have received SMS alerts for all the transactions, there is little chance of SIM duplication.
All said, you have every right to get the matter thoroughly investigated by the bank to establish the sequence of events and provide you satisfactory response.
You can revert to me for guidance, if the fraud is not account of any compromise on your part and your bank refuses to compensate you for the fraud loss.
Regards
J R Mohandas