Data usage disappeared in less than 1/2 an hour

[Anonymous]

Last Thursday (11/5) I got a text from 02 to say I'd used 80% of my inclusive data.less than half an hour later I got another text to say I'd used 100%. I was at work at the time, I had left my screeen on to measure my number of steps whilst at work but don't watch videos, stream music or anything else that uses lots of data. How could I have used so much in such a short space of time?

[MI5]

You may have used it previously but it can take a while for the system to catch up.

[Anonymous]

Thank you for that suggestion but I have never run out of data before. Can't think what I might have done. Thought O2 could tell me but can't find out how to ask

[MI5 · Accepted solution]

They can't tell you what it was used on but should be able to tell you roughly when.
Have you downloaded or updated any apps recently?
Auto play videos in Facebook and instagram can also use lots of data.