Welcome to our community and thank you for your post. I am sure we can narrow down the problem together and get this resolved. It appears that aside from the two phones mentioned, there has also been an Xbox accessing the internet too. The easiest thing we can do to start is do the data test again, you won't need to do it for 24 hours (more than 5 hours is acceptable, some prefer to do it overnight).
I will add data to your account for the test and all you will need to provide is the day and time you disconnected devices/turned off wi-fi, then the day and time you re-connected. The power and coaxial cables should remain connected in order for us to see logged data. Your patience and cooperation are appreciated.