gold ornaments — wrong price evaluation at the selling back of old ornaments

Address: South 24 Parganas, West Bengal

Gold ornaments (with 22 k purity and kdm) was purchased from reputed jewellery shop at kolkata in the month of March 2011. Surprisingly during selling back of the same ornaments to the same shop, they are deducting a sum of 12% on the selling price of 22 K gold on the market value of the same day. As a result we are loosing more than INR 300 per gram with out ant reason.
Kindly guide me whether the gold shop can do the same or not.