Anyone else have huge data usage discrepancy?

So, around a year ago we cut the cord and started streaming all our TV and movies. We kept Cox internet as it is almost the only option where we live. Maybe 6 months ago give or take we started to hit our cap of 1000 GB each month or at least get close. Within the last 5-6 months we also started streaming to twitch. Once we did that our typical usage was around 1200-1500 GB. We were offered a tv package to come back to Cox and our streaming provider had raised prices and also cut some channels so we took advantage of it. So on July 11 Cox installed 2 Contour boxes and a new modem and we cancelled our streaming service effective that day. So we went from streaming TV most all day since my wife does not work, to normal internet usage plus streaming to twitch (not on a daily basis). We should have seen a dramatic drop in our data usage. Instead the day Cox installed the Contour boxes we saw a HUGE spike in the data they reported. It has been consistent since that day. I have multiple tickets in, a tech has been to the house and replaced the modem again. We have been testing by unplugging our wifi router and only having 1 device hard wired straight to the modem. One day we only had the PC connected and it was not used all day but for a couple hours in the evening. Shows 11 GB of data that day. I have worked as a Security/Network engineer for the last 15 years. I changed my wifi passphrase, I scanned all pc's, nothing. I have checked the data usage of both the PC and Mac, everything else is either a phone or a TV or a gaming console. Those have been powered off or not on wifi lately for testing. In the last 30 days the total of the PC and Mac was 850 GB. Cox claims in the last 11 days we used 1,650 GB. I have done everything I need to do to show it is not me. All they keep telling me is they don't know and they are looking into it. This is NOT acceptable. I work in this business. Just saying you don't know and allowing a problem to continue is not acceptable. I would be fired if I said that to my boss or our customer. FIX IT COX. I am tired of dealing with this and you need to do your jobs and figure it out. I am sure others are having this issue as well.