I signed a 2 year contract with AGL which offer me with $100 bonus credit on gas. That I will be credited $25 in every 6 months. I followed all requirements and the last bill also stated that I will be credited $25 in next bill. I finished 2 year contract in Feb and after that I changed to Origin. They denied my last $25 credit due to my leaving. However ridiculous! I fulfilled the 2 year contract, I entitled to get my offer bonus. I will complain to ACCC if this issue has not be solved. AGL is not reliable, last time my electricity bonus initial stated that $20 but after billing they said which including GST so I get only $18.19. And my home address can suddenly change from no 10 to no 25, and then they required me to give evidence!!! AGL is a lier.
Reckon you will find that AGL has done the right thing.
Check your billing did you get the equivalent of $12.50 reduction in every 90 day billing period.
As to getting $18.19 that is the same as getting $20 less the GST.
(GST is added at 10% at the end of the bill)
So $20 * 0.909090909 is $18.19 so similarly $18.19 *10% is $1.81.
Therefore $18.19 plus $1.81 is equal to $20.00.
This is very basic maths and easily explained in Financial Calculations.
You can trust me, I got 100% in my INTRODUCTION TO ACCOUNTING SIX WEEK COURSE at TAFE back in 1993.
Good luck in your endeavours.