HDFC Bank — Asking to pay bills for fraud transactions

Address: Mumbai City, Maharashtra, 400092

My name is nita desai, i got a fake call from hdfc bank about redemption of credit card points, asked for all information, they said you will receive a message with a code kindly give the code, did not realize it is a fake call so i gave the number with was the otp, rs. 9880/- got debited from my account, the fraud transaction was made to buy a motorola phone from ecommerce portal.
I called in for help at hdfc asked them to cancel the transaction and deactivate my card, my card was deactivated and i was asked to fill a form and send it to their investigation team
After sending all details required, i get a stupid mail from hdfc investigation team saying that it was an authorized transaction and we will have to pay the bill for it.
I dint understand if consumer of credit card is saying it was a fraud transaction cancel everything, instead of canceling the transaction hdfc is encouraging the fraud thieves to do this with others
If they could contact the seller from the ecommerce portal n cancel the transaction the problem would have been solved there and there.
So now the thief has already received the motorola mobile phone and we a liable to pay for it.
This is not fair for a customer who is using hdfc services since a very long time.
Kindly help
Contact number - [protected]