I think there was something about this on a legal phone-in on 774 (Melbourne station). The circumstances were different though - the woman had decided she didn't want the ob at the birth but didn't tell him beforehand so even though he wasn't there he was still entitled to the money.

However, I would think that this would work the same as any other 'contract' - you're terminating the contract ahead of the fee for attendance at the labour so I don't think it could be charged. Is there a Medical Ombudsman type place you could check with? Or maybe the Australian Medical Association? Or even your private health insurer? I'd google for you but about to go to bed.

Hope you're able to sort out and swap to someone you're more comfortable with.