A couple of years ago, I had a fraudulent transaction on my credit card. I told my bank who cancelled my card and issued a new one. A week later, I get a call

A couple of years ago, I had a fraudulent transaction on my credit card. I told my bank who cancelled my card and issued a new one. A week later, I get a call from my bank, the person, who spoke with a strong indian accent I had trouble understanding, wanted to follow up on the fraudulent transaction to ensure the chargeback was done properly. He refused to give me any details until I had proven my identity by giving my name and passport number. I was immediately concerned so I refused to give those details. The CS on the phone seemed annoyed at that. I then contacted my bank relationship manager who had no idea if the call came from the bank or not so I decided then that it most likely was a scam. Turns out a week later, my relationship manager told me that the call was actually legitimate. They really didn't understand why having someone from the bank call and ask me for my passport number was a problem in term of security.