Clearing agent that overcharges the customer

This company have an modus operandi. They overcharge on the customs. They use the shipping value and purchase price to determine the customs duties value. Then they add money to the combined cost (already inflated) to calculate the VAT on. So the VAT does not agree to the same value that they calculate the duties on. In my case they added another R100 to the value of the item (already inflated with shipping cost) to calculate the VAT on. They are very sticky to fix the issue and just hold you ransom if you want your item released. Don't even try to call them. But the client has options too. SARS review and tipoff, so see if the amount they are skimming from the customers reaches them. AliExpress repudiation to take them and speedaf off the list of reputable shipping option. Being dishonest does not go around the block that many times.....