British Airways no response

I recently travel to Ibiza from South Africa to attend a multisport event with my son. We decided to travel with British airways because they offer a very good deal when travelling with a racing bike. Everything went very smoothly to Ibiza. When we returned however our we had to transfer at Heathrow to our flight to South Africa. This flight departed almost an hour late because we were waiting for passengers that needed assistance with boarding. I stopped counting at 10, the vast majority of them arrived late at the boarding gate. We allowed 2h for our transfer back at OR Tambo to Bloemfontein which is normally enough but with the delay we just could not make it with the flight at OR Tambo boarding when we arrived at the check in counter. There were no flights available for the rest of that day and as we had to be at work and class the next day we had to rent a car and drive down to Bloemfontein. CemAir did not want to refund us considering us to be a no show and British Airways at OR Tambo said their responsibility ended when we arrived at OR Tambo, the fact that we were late for another airline's flight was not really their problem. I did file a online complaint with British airways about two weeks ago and escalated the complaint since then but sadly with absolutely no response.