Misstated Square footage - off by 50%?

My wife and I purchased a home in 2006, that was listed at 1427 square feet (this was calculated by the seller's appraiser). This is the square footage listed on our mortgage documents, the MLS listing, all of that. When I attempted to contact my bank to see about a ReFi a few weeks ago, they stated, and the... show more My wife and I purchased a home in 2006, that was listed at 1427 square feet (this was calculated by the seller's appraiser). This is the square footage listed on our mortgage documents, the MLS listing, all of that. When I attempted to contact my bank to see about a ReFi a few weeks ago, they stated, and the local assessor's office verified, that the local assessor's office had the property listed at 977.

The reason behind the discrepancy is that the appraiser counted the partially-finished basement as part of the living space, which is a "non-standard and invalid" (words of the city assessor, not mine) practice.

Do I have grounds for redress, either through a professional standards board or the courts?

This home is in St. Louis, Missouri - if you have specific informaton on the practices within the state of missouri, your advice is six steps past welcome.
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