how long was your original reservation for? Sometimes they discount the nightly rate if you stay multiple nights, but if you cancel, they usually charge you one night's stay (Which I sure hope wasn't $421!!!)

As others pointed out, call your credit card IMMEDIATELY and dispute it. The process usually takes 30 days, so you want to start as soon as possible.

2nd, make sure you CALL the facility if you haven't already. Speaking with the head manager or the billing department can sometimes help.

Good luck....