Of course if you are looking back over the last few years, everyone is using more data now. That's because the internet has changed to be more data hungry. Websites today are geared to unlimited high speed bandwidth and, are loaded with background images, foreground images, auto loading video and, even video and/or audio advertisements that never used to be there.
The best way to find out where your data went is to send an email to email@example.com with your account and contact information and, request a usage review. They will be able to give you a better idea of what your data was used for.
There are so many ways to unknowingly use data ....
Websites are changing, Operating systems are making major changes ....
Before you can focus your efforts you need to discover just what devices are using data and which programs and processes are running.
I suggest that you read the following topic and consider purchasing a router that tracks data by device.