Hi Brooke,
(Sorry this is long.)
It's hard to get these surprises.
As a consumer who has had this too, and made some changes to fix this ($ and effort).
I can offer the following.
Firstly, I would call AGL and ask them to look at this bill for you.
They might be able to offer something in the way of an explanation to help you understand this bill.
In preparation for that, get your bill in hand, and the previous bill or two . . .
Check the bill, is it an actual or estimate on the readings ?
It tells you on the bill, read it through.
If you have old analogue meter, they quite often get estimated if the meter reader is not able to take the readings on the day.
Estimated bills are usually a lot higher for some reason, while if paid as it is, and it will balance on on next actual bill, they can be adjusted if it will cause hardship (or even if you just want it reviewed to correct amount now).
If it is actual, check your meter readings and compare to the bill.
I've had incorrect readings over the past 40+ years by electricity meter readers, as well as water meter readers.
This too can be corrected.
If the readings look correct, compare new bill and last bill, is the plan type is same, no demand tariff added, check all the data for any option like peak / off peak / controlled load if you have electric HWS, have these increased dramatically ?
Check tariffs for these, daily supply charge, etc. Same ?
There should be no changes unless a price rise has been made, usually advised by letter or email.
If data KWH is high(er), there must be a reason, more use of something, maybe something faulty, see if you can isolate what it could be.
This can be done by taking a couple of days readings and noting down, leaving one high use appliance off of a night / day, and see if the meter eases back, repeat.
If tariffs have changed, not much can be done there apart from check it is a recent legitimate change on your plan, compare AGL plans / tariffs to ensure on the best one for your homes energy usage patterns, and if that fails compare other options on energymadeeasy.com
An important thing here is don't rush changing energy companies !
Believe me, I have looked at this, and I can say from experience looking at energy pricing across Australia, sometimes you can benefit from change, and other times you can be paying more.
Reasons are :
States and regions can have remarkably varying levels of competition.
States and regions can have remarkably varying plans and tariffs.
States and regions can have varying options for times of peak / off peak / time of use / demand tariffs, etc.
You have to find one that suits your own power use best for your location.
Here in SA I have found although there are a good number of retailers, there is very little real competition, little difference in pricing.
Some have higher tariffs but lower daily supply charge, others are vice versa, and no real difference to bills.
I can say that in looking at things like power company offers, solar offers etc that pop up for me on FaceBook, power cos are on there offering this, that, great looking deals, but look at the comments, so many unhappy consumers out there.
Best of luck with it, hope you can get to the bottom of this and keep the bills under control.
