Shock offload from flight, total lack of information

Are you Flying from South Africa to Europe with British Airways in transit through the UK ?? then beware of this **** .......When you book your flights online , no where does it alert ,or inform you that you require a "TRANSIT VISA" for Heathrow airport....you are all paid up and ready to fly on holiday..You even check in Online no problem...and when you arrive at the airport to Your Horror! you get offloaded off the flight because you do not have a transit visa for Heathrow !!!!! You then have to claim a refund at least an hour before the flight departs, of which you will only receive about half your money back !! what a **** !! surely with technology once you book and state that you have a South African passport there should be a pop up that tells you you require a transit visa....there is nothing of the sorts....just the shock and dismay when you arrive for your flight....and this is happening almost daily with passengers from South Africa ! Someone needs to take responsibility for this lack of information and ridiculous system robbing passengers from SA ! I have spoken to many travelers and no one is aware of this Transit Visa ?? Fix this please !!!!!