Update 2. I've received my first bill which was estimated. Nothing near what my actual usage is, which is why I originally posted on here. I have called AGL and the guy was really helpful, however he let me know my original case had been marked as completed- even though they are still estimating my bill. He has raised another job to get it sorted out. I've also contacted the Energy and Water Ombudsman SA to hopefully help get it sorted out.