Are you talking general credit or solar credit ?
Apparently regular credit (very low power user with govco credits, perhaps bill smoothing excessive credit, etc) can only be claimed by contacting AGL support.
Solar credit can be also claimed like that too, OR you can "arrange to be paid periodically" . . . not sure how often, I know you can have an yearly anniversary date for credit refund to your bank, it could be as arranged too, perhaps twice a year or even quarterly.
* I just found online you might be able to request a credit (unless on a payment plan)
https://www.agl.com.au/help-support/billing-payments/request-credit-refund
To request a credit refund or check your refund status (after at least 7 business days) use the chat icon to chat with us in My Account or the AGL app, or contact us.
Also, further down the page . . .
My Account
If you have a credit that’s eligible to refund online, a Request a refund link will show under your credit balance in My Account. Select Request a refund and follow the prompts.
When to expect your refund
It depends on the payment method your credit is refunded to:
- Card: up to 3 days
- Bank account: up to 4 days
So maybe try that next time ?
Not sure if it will work but worth a shot.