..
Sounds odd, but easy to fix.
You have access to the meter, and it is analogue* (if needed to be read), so you can go to the app, or on the web when logged into your account > Usage page > Enter a meter read > enter your figures there and submit.
Reading your meter . . .
https://www.agl.com.au/help-support/moving-meters-connections/read-your-meter
Pretty sure you will need to call the AGL main phone support https://www.agl.com.au/help-support/contact-us and let them know you have submitted correct figures via the app, they should be able to reissue and adjust payment date.
* Some digital meters also need reading, when they are not able to upload info due to some rare connectability issue.
In this case, it might need reading by a contractor as you might be on TOU tariff which you can't read like an old analogue meter, and I think they download the data with a special tool.
