Hi, there. I'm so sorry for the issues surrounding data usage and I would like to help. If you disagree with the Cox Data Usage Meter, there are many 3rd-party meters available. It might be worthwhile to compare the metrics from a 3rd-party Data Usage Meter with our Data Usage Meter. Our meter has been tested for accuracy. Netforecast, an independent third party, has also provided an independent report (PDF) verifying accuracy. To learn more, go to https://www.cox.com/residential/education-center/internet/data-usage.html. As you've mentioned your daughter and two children recently moved in, it may indicate some sort of server application. Most often, it is a BitTorrent application that may be running unbeknownst to you and serving files to the torrent network. I might recommend checking all computers for Utorrent, BitLord, Bitcomet, Shareaza, etc.... and uninstalling them if found. Here is a link to a Wikipedia article that lists most of them by name: https://en.wikipedia.org/wiki/Comparison_of_BitTorrent_clients.
In addition, cellphones may be running "Popcorn Time" or "Showbox" which are also torrent clients. Also, if you have a Firestick for your TV, they may be running Kodi, which is also a torrent client. I hope this helps you get to the bottom of the issue. If you need us here, we're glad to assist you. Please email us the physical address and any other pertinent information to Cox.Help@cox.com with your name and a copy of this forum message. We are glad to help.