Hi @davinaj , Sorry to hear you've had an unpleasant surprise with your bill.
I can't check your account from here, but even with no gas appliances being used there would still be a fixed supply charge for the connection - this is the charge for supplying gas to the address regardless of how much gas is being used. It would apply up until you requested cancellation and disconnection of the service.
For more info, check out What is a supply charge? or the Australian Energy Regulator's page on Tariffs and fees.
If you get in touch with customer service via phone or chat, our agents will be able to help investigate and explain any charges on your account. You can also log in to your account and check out your full billing history, or click "Message Us" to get in touch with any questions.
Finally, if you're still unhappy with the response you get from those options, you can submit a complaint here.