Over-inflated customs invoice

FEDEX made a mistake on my customs clearance and over-inflated my customs clearance Invoice. Nos they do not want to refund my money. I have always imported from China using FedEx. I always import for small value below R3000. The maximum amount I have ever paid for customs clearance is R600. Now I have imported again from China for a value of R2300 and Fedex send me an invoice of R1625.03 and asking me to paid within 48hrs otherwise my goods will be destroy. I have found out that Fedex have made a mistake on the country of import, they said that I am importing fro United Emirates. I believe that this might be the reason why my invoice is so high as all my China customs invoices as always been below R600. They do not want to address the matter or to provide clarify on why my customs invoice is so high (more than 60% of the commercial invoice value).

Does anyone know how to escalate customs issue with Fedex? Please help.