They haven't billed you that, but I agree, the estimates for analogue meters is usually very high, and this is despite AGL saying it's based on past similar periods.
There should be a meter reading contractor out before your next bill is due, then they will send you a bill based on actual usage.
If for some reason it's an estimated bill (no access to meter, dog present, etc) then you can upload your own reading at any time to have it recorded.
At my workshop, the gate is often locked, and there used to be a dog present (docile), but the meter reader would never go back to the box to take the 7 shed readings.
In 2022, I got a bill for $9245.78 for the workshop, when at the time it was usually $200 - $300.
Was quite a shock !! (no pun intended)
Took a call and a meter reading to sort out.