Hi IreneS, We're sorry to hear about the situation. It would be best to understand the source of the usage to get on top of this issue. I assume you have a smart meter at the site and the usual configuration is that your energy distributor/metering coordinator relays your usage data to AGL, which then gets reflected on the AGL app and the costs associated with it. Unfortunately, changing retailers isn't going to resolve the underlying issue as your energy distributor will still remain the same and the way they report your usage will remain the same.
Your standby devices and devices that runs continuously (example your fridge) will continue to use electricity even when you are not at the site. However, this will be consistent and there shouldn't be a spike in usage when you are not at the site. An electrician perhaps could give you a better understanding of where the usage is stemming from. Also, please visit https://www.agl.com.au/help-support/financial-support/energy-saving-tips to get some useful energy saving tips. Cheers, Deepesh