How did they get the account number and amount for the balance transfer? If you entered that info when applying for the card, you did authorize it, so you do owe it.
Did you overlook transfer fees in the fine print, or not get the interest rate you expected? I recently figured that it would cost me less interest to pay off a 9.74% card in 4 months, than to use a 1.99% teaser check with 3% balance transfer fee.