Caller claims to be from United Airlines and wanted me to fax her a copy of my credit card statement to verify credits that had been returned to me. She then gave me a bad email address. Never give out personal info unless you're absolutely certain it's to a reputable source.
The exact same thing happened to me and I got a letter too from these people. The letter was not on genuine United Stationary and furthermore had grammatical errors that a major US company would NOT make.
I completey agree with the peron above. BE CAREFUL!!