This is NOT a legit number. The people saying here that it's really Citibank must be with the scammers -- it is indeed a scam number. I have received a number of calls where they left a message saying it's Citibank's fraud hotline or somesuch thing and to please call back. I have never opened a Citibank account in my life. Don't be fooled into imagining it must be legit just because some previous posters here insist that it is. It's clearly a criminal operation. Again, I've received a number of messages claiming to be from Citibank fraud center at various times - not all within a couple days. I do not have a Citibank account, never have had one, and have never later received a callback apologizing for accidentally contacting me b/c I'd been called erroneously or anything of that nature. This is NOT actually from Citibank.
I got that call too. The lady on the phone claimed that she was from Citibank and told me that my Citibank credit card was blocked. I felt suspicious and told her that I don't have time to talk and she said, "Call back when you have time." Then I was smart enough to login to my Citibank account online and checked my credit card status and it did show the message in red indicating: "Please call the customer service to avoid interruption on your credit card transaction." So, I did call them (other than the number on my caller ID) and I do recall that I have made the online transaction for Yahoo subscription. Actually, Citibank just wanted to verify to make sure that I did make that transaction online for our protection against fraud.
Thought I just wanted to share with you all one bit of advice. It is always wise to call or check online with YOUR bank if you're actually have any accounts with them and DO NOT call any other number who called you. That's right! It could be a SCAM but you never know.