The only way you can convert from EASA to CASA is if you hold a type on your company authorisation for at least 6 months. So if you hold say 5 different types on your EASA license but only one on your company authorisation then CASA are only interested in what you are recent on i.e. what is printed on your company authorisation.
If you have no types on your company authorisation then there would be nothing to convert. Pretty crappy but I'm afraid that's how it is!!