If a person used Firefox, they could well expend all their mobile data, just by having an Optus page displayed for a few hours. If you don't have a bandwidth monitor, you can see it in the Windows Resource Manager.
Are your sure it's not all going to MIA Sphere.
MIA Sphere could be an alien abduction hub, for all I know.
I have managed to get rid of the problem by installing my old browsing friend "Disconnect"... I had to get rid of it when Firefox introduced Quantum 58. Disconnect just doesn't let your browser connect with 3rd party tracker websites. It's blocked part of 247, but not all of it.
247inc is the customer experience licensee of the software we use for Live Chat.
The Live chat prompt does pop up now and then when you're browsing the Optus Website.
I imagine that's why it's embedded within most of our pages on the site.
That would make sense. The web page keeps a connection alive and sends a small header to 247, every few seconds. In my case, for a few days, it had decided to upload continously to 247. If I'd been quicker on the draw, I could have gone to Firefox web developer tools -> Network, and seen what was happening. After installing the Disconnect plugin, the problem went, even when I disable Disconnect.