Devices usage

I have me and my 3 kids' profiles on my account plus the household account  They all say no devices connected except the houshod one  but when all the profiles are shown together it shows what percent of internet we have used.   I called in to Xfinity twice and spoke with someone for about an hour each time and they had me try a bunch of things then they basically said they didn't know.  My kids are always on their phone, palying video games, whatever, and it always says "no time online today".  How do I fix this so it actually works?