Ok, cheers @Cat868 sounds like it's a long term issue, and needs to be sorted out finally.
I think your strata management needs to be brought into check on this policy of no allowing access to at least service contractors, such as meter readers.
From google AI to > strata management and rules for allowing meter reading . . .
"In Australia, strata property owners and occupiers are responsible for ensuring their meters are accessible to utility companies for reading, maintenance, and testing.
This involves maintaining clear paths to the meters and resolving any obstructions.
If meters are not accessible, retailers may issue estimated bills, which can be adjusted later.
Owners can also provide their own meter readings (self-reads) by contacting their retailer, or by arranging for a master key to be made available for utility locks on gates or meter boxes."
Hopefully you will find your bills are not underestimated . . . in the vast majority of cases, AGL's estimates are usually on the high side, so who knows, you might end up with a substantial credit, a kind of forced, but unwanted, savings plan for the years of estimated bills.
And yes, I guess of the strata and AGL cannot work this out, the ombudsman in your state might be a last resort.
