Hello Graham,
No sure why you can't talk to someone representing AGL . . . I have called them several times in the past months, and although wait times can be a bit prolonged by phone, it doesn't seem as painful as other businesses that operate automated / call type centres.
The number is 131245, or you can try Chat via the website contact page, I have used this and just do something on the computer to keep me busy for a short wait . . . https://www.agl.com.au/help-support/contact-us click on Chat.
I see on the AGL site, when logged into the relative account, you have the option in Wallet to add a payment method.
It's very likely direct debit is possible to set up here too.
https://myaccount.agl.com.au/settings/mywallet
You might have to set up the AGL account and login etc for your brother.
Good luck with it however you decide to go about it.
