I suggest you talk to AGL via the phone or their messenger.
If your bills have been estimates, when you left a full reading would have been undertaken and the result is your final bill.
Thanks for your message.
I tried to reach the customer service but they don't reply to me, they leave me on the chat waiting for the resolution team to solve my issue but nothing happens.
This morning I got another bill, but this time is higher than the previous one... $800!
Plus on the bill is written that the bill period is 31 days (13th of June - 13th of July) but I left that property on the 24th of June.
I think I'll pass it to the ombudsman.