The scammers called several days in a row to report suspicious activity on my Visa or Mastercard. They wanted the first 4 digits of my credit card number, which I gave them. Then they wanted my full debit card number to enable them to block future false charges to my MC (right, this sounds likely!). I gave them a false 16-digit number, incorrect expiry date, false 3-digit code on back. Then I got forwarded to the supervisor who has the authorization to secure my account.
I had visions of him typing busily to sign onto my account, and he was probably going to help me change my password to make the account more secure. But we didn't get that far, because he must have figured out I gave him a bad card number, about the time I asked, "If my Visa is the problem, why are you so interested in my debit card?" He hung up.