First of all, you have every right to be upset.
Second, it's nobody's concern whether you have $60, $600, or $6000 in the bank, how can that possibly tell them whether you can afford a Disney trip, and how dare they say it?! NOYB!
Third, don't email. Write a letter and mail it. Here are several addresses you can write to. When I had an issue, I wrote to two addresses just in case, and I got two phone calls. One was very concerned, and I even got something I wasn't asking for. The other wasn't as concerned, but listened to my issue. Here is a page from Deb's AllEars with several addresses you can use:
http://allears.net/pl/contact.htm
Good luck. I would certainly let them know that this error on their part put you in a bind. Just don't be excited and upset when you write it, do it calmly and factually-leave emotions out of it.