Aust Post Shipping -Parcels and Letters?

Hi,
I have OC 3.0.2.0. I have the Aust Post Shipping API set up fine and working well.

However it seems to only do parcels and not letters.
If it cannot be added how can I add a shipping option to a product that used the API and also an option for letters.

The unit can be sent as a large letter $3.60 no track but goes as a Parcel $10.60 with track.
Customers complain of the ship cost.

How can I do this ?
Thanks

You were not clear about the aust post shipping module. is it default or you downloaded it from a third party? is it default you can check in the forum, You will get the solution.
Also contact that developer or company from where you downloaded it, they might have the solution for you.