Visa requirements not highlighted

On a flight from South Africa to the UK, landing in Amsterdam and Paris, I was denied boarding as I did not have a Schengen Visa which I was obviously not aware of. Had I been aware of this, I would not have chosen that particular flight. I had a UK Visa. I was in transit and not leaving the airport. When booking on line, a red box is highlighted and flashes TWICE warning one of children under 18 years and the requirements. Why then does it not do this if a special Visa is required???? I can say why - so they make extra money when many passengers have had to either pay in or cancel and lose thousands! I had to pay in R5000.00 to get to my destination and Air France simply could not care and say it is the passengers responsibility to check on Visa requirements. I could not afford this extra but also couldn't cancel my trip. Only having flown direct to Heathrow in the past, I was not aware of any additional visa requirements. I had also paid for special seats. This ticket ended up costing at least R6000.00 more than another airline! I phoned Air France in the UK and have sent e-mails to them and they simply couldn't care about the odd person who looses out as they have so many passengers. I was told by an employee that hundreds of passengers have this same problem and nothing is done about it and they are also really upset and do not get any compensation at all. What a disgrace Air France is and I shall certainly never book with them again and shall tell everyone what shocking and no-care attitude they have. A well deserved and exciting trip was ruined by them and their lack of service.