Misleading / False Services

We booked a flight on the FLYSAA website for our son Rinaldo Morgia, departing Port Elizabeth, arriving OR Tambo. Upon him checking in he was told he is flying with MANGO Airlines and NOT SAA. This we find totally UNACCEPTABLE as well as the excuse that we should have checked out the ticket where it is mentioned the flight is operated by Mango. If I wanted to fly Mango I would have booked on the Mango website. We did not see that and find that wording added at the bottom of the ticket as part of the text UNACCEPTABLE and TOTALLY MISLEADING. The flight nr clearly stated SA 2062. Why does it not use the MANGO flight nr's to point out you will be flying MANGO Airlines? We also had NO CHOICE to pay extra at MANGO Airlines for his cycle bag which is the MAIN REASON we vowed NEVER to fly MANGO again. Should I not have been present at the airport to pay the additional charge, our son would have been stranded, as the personel behind the counter was EXTREMELY unhelpful and could care less to assist us. I feel as a consumer I was MISLEAD by not be warned upfront BEFORE I PAID that I was going to fly with MANGO and that there could be additional charges as their policies are different to SAA.