Standard Chartered Credit Card Is Charging Money For A Unauthorised Transaction.

On 20th Nov 2019 I got an SMS of deducting USD 328.27 from my Standard Chartered Credit Card. But before that, I neither got an OTP for this transaction on my mobile phone or in my email id. I reported the same to the bank and then the bank blocked my card and started investigation for this unauthorized transaction and the bank comes up with the following report "A review of our records indicates that the transactions were carried out on a 3D secured website. Post successful validation of your card credentials and the OTP which was sent to your registered mobile number, the said transactions were approved. Hence, we are unable to initiate any further investigation in this regard. We request you to effect the payment towards the same to avoid levy of financial charges on your card account." But I DIDN'T RECEIVE ANY OTP IN MY MOBILE OR EMAIL. I also registered the same in cybercrime.gov.in Acknowledgement Number: 21912190004719 I need to know how the transaction happens via a 3D secured website without asking OTP from me. Also, I don't want to pay the bill for an unauthorised/fraud transaction.