I have seen many people pass medical&security and sit on waitlists for months ( my best friend waited 18months ! ) and then get dumped. But...to get rejected straight away obviously means something was wrong with your medical or security. There is no way you can claim as per your first post that nothing was wrong with your medical because you will never know the results of that examination. They are confidential and passed straight on to QF medical.
I'm baffled also as to how they recruit also, I'm one of the lucky ones who is already in - but in this case I believe there may be something wrong with your medical.
Don't give up. EVER.