HDFC credit card - Lapse of HDFC bank led to fraud

This is related to a fraud transaction that happened on my credit card ending ****. I stopped using my credit card in ****, however my card was still active. I moved to the US in Sept **** and did not use my card at all for a year. The card was physically with me in the US. HDFC charged a one-assist fee, which I was disputing for months. This happened in June ****. I kept disputing the charge and noone was helping me. When I complained about this on Facebook, am HDFC employee messaged me on Facebook and requested to speak with me. He seemed to know exactly about the issue and also had my charge details. He took my credit card number. Later, I realised he was a fraudster. I was not worried because I was sure I would get the OTP on my phone. However, I found out that HDFC had not actioned, my change of phone number for credit card, when this fraudster succeeded in making purchases online. To my bad luck, my old number was in use by someone else in Gujarat (**********). The fraudster called that person and got the OTP and made transactions worth Rs. *,**,***. I managed to get Rs. *,**,*** back from Flipkart, but Amazon is pending(case filed through Voxya). For months, I kept following up with HDFC, with replies from Amazon stating refund has been made. They have not made any investigation into the matter. And in a very unprofessional way, they deducted my Rs. *,**,*** from my bank account! They did this, without replying to any of my emails about this issue. Its as if they did not even owe me an explanation about the lapse from their end!!! They just went ahead and deducted money. I demand my Rs.*,**,*** back from HDFC. If they had actioned my change of phone number request, this would have never happened.