The usage figures can be delayed by up to 48 hours (so the data usage may have been earlier than you though), but it does seem like a large jump. Things that can cause a large change are operating system updates (occasionally they stop and have to restart - I have seen cases where they repeatedly do that and use a lot of data) - check computer/phone network stats to see if they are reporting anything, streaming devices left running, synchronising data to cloud services.
Otherwise, you can request that it be checked by sending a message by either:
- the My Telstra app on your mobile
- logging into your account via the telstra.com.au website
and then go to the Get Help tab and click on the blue icon at the bottom of the screen (labelled Message Us on the website, icon only on app). If the bot doesn't understand the query, type "Speak to a consultant" and you should be transferred to the queue to chat with a human. It can take a few hours to get an initial response. If you use the app, you will get a notification on your mobile when someone responds.
Never be afraid to back yourself when trying new things, just always make sure you have 3 escape routes if things go wrong.
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