Huge FBA international shipping Charge China to USA

Amazon charged me “FBA international shipping” of over $1000 as additional charges to a shipment that should of cost $750. The $750 charge is on the statement, but so is this additional charge. Been around the block with support and essentially the answer is suck it up with no justification or breakdown, I am suspicious that the partnered carrier BSI E-COMMERCE AIR & SEA LOGISTICS LTD (never use these people as they actually ripped open 50% of my stock) has just put in a fat invoice and helped themselves. BTW there are no tariff duties due on my product. Anybody else seen this?