You paid more than you were supposed to on the Hero. Standard import duty for electronics is VAT, so 14% of total value (cost of item plus shipping costs, if I recall). This only applies for a package worth R5k or more.
I last looked up the documents with the DTI yeaaars ago, but back then, cameras and videocameras attracted VAT by default as they had the capacity to 'capture an image', and so were deemed capable of 'capturing television signals'. Remember all that drama about computer monitors attracting VAT in SA now on account of their capability of showing something broadcasted on TV?
Best practise is to have information at hand direct from the DTI on what import duties are for whatever it is you're importing, and to reference it when someone at the customs office is trying to rip you off.
I looked the info up since I was working for eDimensional for a while and had received as part of my payment a set of their headphones, LCD shutter glasses and the VoiceBuddy software, the total package which amounted to R1.4k total value, shipping included. At the customs office, we got a call from someone that refused to give their name that said customs would be R1.45k on the package. My mom had been handling the call when I walked into her office, so I asked her to give me the phone, pulled up the relevant info and referenced it - the woman on the other end just put the phone down. Two weeks later, we got a call from the SA International Airport's customs office again saying there was a package there marked as 'unclaimed by recipient' that wasn't assigned to anyone at their offices that would be returned to sender if we didn't claim it. We explained what had happened in the last call and were told that the person that was trying to get the money out of us last time was doing so unlawfully as that package wasn't supposed to attract customs at all.
ie: Extortion at SA customs. Has been like that for years now.