Overcharged taxes

Been gettig deliveries with buffalo without any issues but lately they have just increased taxes without any explanation or how they come up with the figure. I don't understand how goods that cost less than R1500 and less than 3 kgs can have a duty of more than 600. The last 4 deliveries have been the worst and i doubt i will ever order things from shein again because of fear over being overcharged by them again.