Disappointed DHL

I ordered a gift from Thailand. The weight of the package is approximately 3 kg. And Service charge of DHL is approximately R3200. This part I can understand. But what I don't understand is, clearance here in South Africa charged me R2300 for tax/duty. For whatever reason I still haven't got an answer. The items in the package are less than R2500. But clearance charged R2300 for tax/duty. Anyway , I paid in full amount.. But there are even more worse, In the morning I have got sms from DHL saying that my package was pre-checked at custom and may be delayed for delivery. I would like to know DHL is the most expensive service charge but why DHL is delay for delivery? And the tax rate is the most expensive in the world But the delivery service is the slowest.