It is a conditioned reflex with most people to believe that letters written on important-looking notepaper or information generated by computers must be right. Not so. You should believe no one and accept nothing.
A few years ago, my bank wrote to me explaining that, due to an error, they had incorrectly credited my account with £100. Although this proved to be true, I decided to deal with them as they would normally deal with me. I sent them a cheque for £90 and explained in a covering letter that I had deducted £10 in respect of my administrative charges. I heard nothing more.