Paying for excess luggage from an international to domestic flight

I requested to have my bags send straight through to my destination which was East London, unfortunately at the airport in Dubai they were only able to sendy bags to Johannesburg. I flew with Kenya Airways Dxb - Jhb. An international luggage allowance is 2 bags of 32kg each .

My flight from Jhb to East London was via Kulula.com

I got my 1 bag and went to check it in at the Kulula counter to find out the luggage allowance is 20kg.....my 1 bag was 29kg.....I had to pay R330 for the excess 9kg inorder to get a boarding pass for the flight.

I honestly don't think this is fair after I have spent almost R2000 for a one way ticket Johannesburg to East London and then i have to still on top of that pay for excess weight when I have come from an international flight. Keeping in mind I could of had 64kg with me but I only had 29kg......