Thanks for your post!
By the sounds of things, I don't believe you were set up on monthly billing as requested I'm sorry to say. However, if you came aboard approximately three months ago then a quarterly bill will be right around the corner.
The good news is is that monthly billing is very easy to set up! Simply log into your AGL My Account, navigate to the 'Billing' tab and then click 'Set up Monthly Billing' on the right hand side of the screen.