CHEMPET branch demanding additional payment

Chempet branch I ordered a package from a merchant in USA and it took about 3 months for DHL to deliver. I allegedly was not home, so DHL dropped it off at the closest post office, CHEMPET. Chempet charged me an additional "customs" charge of over R700 (For a R1000 item) I know for a fact that the customs charge was included in the payment to the merchant, and DHL intended to drop the package off with no additional charge, so this means someone at the post office is trying to make a quick buck and blaming it on SARS, knowing that one can't argue with SARS. This is the second time something like this has happened to me at the SAME POST OFFICE.