online error for older kids under 16 travelling with kids under 12

yesterday I booked a flight for my 2 kids travelling from Jhb Hla to dbn (ref VYRXOT) and when the kids arrived at the airport they were not allowed to get in the plane because they needed to be accompanied by someone over 16. Ok my question is, why did the kulula online booking system allowed me to process the book without giving me a notice of this. I believe that the system should have stopped me into continuing with the booking cos it was not a valid book since im booking for 2 kids without an adult over the age of 16. I then went to test this with mango airline and guess what.....(IT DIDNT ALLOW ME TO PROCEED WITH THE BOOK COS THE KIDS ARE UNDER THE AGE OF 16) this means kulula will allow us to make mistakes and not protect us as customers not to loose our money. I demand a refund cos this is a error that kulula should make sure that the online booking shouldn't allow, kulula should also take responsibility when it comes to sure issues. I demand a refund