I'd advise you to contact your credit card company and put in a complaint. They will initiate a stop payment on this item and put a hold on the transaction.
You will then need to submit your written documentation from your independent appraiser to contest the sale. Be CERTAIN that the appraisal is from a true independent appraiser (one that does not buy or sell jewelry of any form) Other wise the credit card companies will conclude that the appraiser is trying to "spoil the sale" and perhaps sell you another item. The jeweler will then have to submit their documentation to justify what they sold.
This is a big problem when dealing with some of the larger corporate stores. They are fine and dandy unless there is a problem. Then the run-around starts. They know there is a time limit that the credit card companies must adhere to before they can reverse charges.
First step is contact the credit card company and submit your documentation.
Hope this helps