Transit

Dealing with British Airways and trying to get a straight answer on a question for visa purposes on a flight is near impossible. We have a connecting flight with BA and no one can tell us the flight details when in transit to ensure we have the right paperwork. In short we need to know with a flight from SA to UK in transit to Amsterdam, can we stay in transit at Heathrow. Logic and all the government sites ask in no uncertain terms if we need to go through passport control. You only need to is you leaving the airport, or have to pick up your backs and check it in for the next flight. No one at BA can answer these questions it seem so we thinking is it safe to fly with the lack of information on hand.