Much depends on the "shape" of your Network.
Is it a single computer connected directly to the modem or is a wireless connection involved?
What types of devices do you have connected?
If Wireless, do you have an Exede wifi modem or do you have your own router?
Do you stream a lot of video content? If so, at what resolution?
Are you running Win10 as an operating system?
What browser do you use by default?
Do you have browser extensions installed to block Ads, Flash content and HTML5 prefetch?
Have you disable video Auto-Play in your browser settings?
After answering the above we can look at how to determine what each device is using data and from that, how to stop or at least slow your rate of usage.