Fraud Calls — Unauthorized credit card transaction

Address:

Chennai, Tamil Nadu, 600073

Sir
My husband mp vasanthkumar received calls from mobile no +91 [protected], +91 [protected] on 9th march 2016, 10th march 2016 saying that they are upgrading his rbl(Rathnakar banking ltd)creditcard to higher limit.She also told his creditcard details including cvv and asked him to verify the otp just to transfer the reward points to his new creditcard and he did so
The same things happened consecutive times and he has been billed for 30, 000/- in his creditcard account
He couldnt even findout that its a fake call, it was that much professional.
How an anonymous person will come to know his creditcard details when the creditcard is still with him?
He has raised a dispute with rbl bank an got a reply saying he is liable to this an he have to pay his creditcard bill on due date
So plz investigate in this matter asap
Attaching local police complaint acknowledgement, dispute form, will upload the creditcard statement once it is mailed as it is blocked now