You are best talking to AGL on the phone direct, they will direct you to the main contact page here in general.
www.agl.com.au/help-support/contact-us
Most likely, you were put onto some sort of different tariff / plan, and it doesn't suit you or your households usage.
They can work through options that may be a lot better for you, a lot depends on if you have old analogue or digital metering, plans can vary a lot more with digital smart meters.
Getting on the right plan with the right retailer is critical now, it's easy to be caught in a bad billing situation.
Good luck.
