Jordo, check when you get a chance that your payroll group has all the right documents relating to tax. You should have been required to furnish them with some information to prevent large tax payments being automatically drawn from your weekly earnings. Normally they want your tax file number, but as your new in the system, they will need some other data from you.
And regardless of your skills, if they have indicated $X per hour, they should be sticking with the agreement. And the agreement doesn't need to be documented to be binding, so warning for you on that front, make sure you have documented notes to support your meetings from first day interview and from then on in. Its the safe way to operate.
Hope you get it sorted.
Mineral