Kulula pathetic servive

My son had a flight from Lanseria to Durban on MN511 on 01-12-2019 at 10.25 am..He was in the check in line at 9.25am and advised by a kulula manager to follow the online check in line. He told the manager that he had not done online check in but manager insisted he follow that line...while waiting in the line the boarding time elapsed. My son missed this flight. There were no more flights from Lanseria. He had to arrange transport to OR Tambo and pay R1450 for another flight. This is ridiculous and no fault of his. We have complained to Kulula and we have not received any feedback. This is completely unacceptable.