Basically, to sort out any confusion, I'm suggesting the scenario could have panned out like this:
Australian couple engage agency to arrange a surrogate. Money is given to agency.
Agency arranges surrogate, with promise of payment.
The implantation (not sure that's the proper word) is carried out and the pregnancy begins.
It's discovered the pregnancy is twins. Agency promises surrogate more money (at this point I don't think we know if the Australian couple was charged any more?).
It's discovered the boy has Down's Syndrome. The Australian couple ask the agency to ask the surrogate to terminate the boy.
Agency asks surrogate, but surrogate refuses, as is her right.
Agency, afraid to lose "business" (ugh) or money, tells couple the baby has been aborted.
Twins are born. Agency collects girl, gives girl to parents. Parents go home with girl, unaware that the boy they thought was aborted is alive. Agency pockets most of the money and screws over the surrogate.
This is what I'm saying MIGHT have happened. OR the parents could be scum of the first order. I don't know. But the addition of a surrogate agency, which we don't know the name of, adds a lot of questions into the mix.