It sounds like you didn't get the discount. They should have charged you a lesser US dollar amount.
You may want to call back and go over the details again - and be sure you're using your Visa.
Details from mousesavers website:
Canadian Resident /Visa Card January-April 2005 Dream Maker Package
Canadian residents who use a Visa card can book a specially-discounted Dream Maker package for check-ins 1/2/05-4/16/05. Discounts will be extremely limited or nonexistent for check-ins 1/14/05-1/16/05, 2/3/05-2/5/05, 2/10/05-1/12/05, 3/11/04-3/13/05 and 3/17/05-3/19/05. There is a three-night minimum with this offer.
This is an "at-par" offer based on the premise of paying in Canadian dollars instead of US dollars, thus gaining a discount from the exchange rate. You will actually be paying a discounted rate in US dollars, based on a set rate of .72 US to $1 Canadian. For example, if the regular total would be USD$738.00, the adjusted price would be USD$531.36. The amount is charged to your Visa card in USD and then converted to CAD by the credit card company at that day's actual rate. There may be additional exchange fees, depending on your bank policy. Rates will vary by season.
Silver Plan add-on is available with this package, but the add-on portion is not discounted.
You must book by 12/1/04. You must book and pay for the package with a Visa card. Proof of residency required at check-in.