Kulula.com conning pasengers on connecting flights

On 10 May 2018 I chose kulula.com as service provider to travel from Durban to George via Johannesburg. The first flight would be on a British Airways plane and the second on a Kulula plane. Arriving at Johannesburg I headed over to the oversize / fragile claim desk and found that my item wasnt there. I recieved a refference number and was told that they would contact me. I havent heard from them since and am still waiting for a response to an email communication. Whilst checking in for my 2nd flight, I was now told that that my bag (@23kg) was now overweight and that my hand luggage (a bag I've allways used as hand luggage ) was oversize. I was now being charged an additional R745!!! For an extra bag and overweigt bag. (That is half of what the total ticket for both flights cost) How is this possible. I made single booking using kulula.com. I feel that this is this a way of conning passengers on connecting flights with the extra charges. I am verry dissapointed to say the least, and deeply regret making use of kulula.com