Typically it's a large and infrequent software update which does this. Recently I've also noticed Facebook and websites stream videos at around 256 KB/s in the background when I'm only reading text.
I highly recommend to search online to identify the option in the settings to view which apps have consumed your data, as has already been recommended.
In my case, it was Chrome consuming the bulk of my data in recent usage.
Hi James, no haven't checked but nothing has changed and my data never ran out before ..
Android & iOS devices have a data counter within the connection settings menu that will give you an app-by-app breakdown of where your data & WiFi has been used - you can often set the counting period to match your billing cycle to further assist.
This will often identify the cause of increased data usage, otherwise check whether your phone's software updates are allowed to use mobile data or are restricted to WiFi only.
The vast majority of "where has my data gone" queries are answered by these two scenarios.
