DATA USAGE ACCURACY

You were on the other thread. I didn't recall references as such there but I was not following it that close. 

Maybe the behaviors are related? You might look in one of the other community sections as well. Like accounts and services. Yes, when you need to watch the budget and the tool does not work right that is a bit of a problem. Hope they get that resolved soon.

Do you have any streaming devices that don't get power from the TV's usb port? Those can keep streaming even after you turn off the TV.

I run a Harmony hub and turn all the connected systems off when not using the TV and I power down the Fire Stick so the devices tend to have to start up all over again. 

If you disable the router then the TV has no way out. So, turning off your gateway takes the network and all devices off the internet. 

I was commenting in the "other thread" that my usage totals have not been updating (still haven't been BTW}….but I did notice that when they were updating, the time-stamps of high data-usage did not seem to be accurate.  Sometimes they were, but other times when I was watching a 1080p movie at a certain time. the time stamps would sometimes not show it.  Over the course of a day or two, I "think" the data averaged out to the correct totals, but didn't think the time stamps were accurate.  Now, for me, they aren't updating at all.  So, yes, maybe they are related issues.

It may be for certain types of accounts their reporting is not accurate. I elected the Magenta 1.0 and have 6 lines, which includes the home internet line, and with the T-Mobile app on my phone it seems to be correct. The bill has been consistent and the same since we joined T-Mobile with the phones and home internet gateway so from what I am seeing things "appear" to be recorded at levels I don't believe to be off. I am not really that tuned into all the different plans they offer. I explained exactly what my objectives were and looked over plans back then and decided upon the Magenta 1.0 which meets our needs and is much less expense than any of the others that were available to me at the time. When I compared it to how we had been using prepaid cards and mediocre phones which was a repetitive bother to deal with the card loading it actually was better to go with the family plan we have. It was a set amount each month that worked with the budget. 

The T-Mobile home internet plan with the gateway is unlimited but is subject to throttling when traffic levels are higher. There is a seniors plan for 55 and older. The home internet, if available in your area is $50/month with auto pay. There is a special they are doing now with the home internet but has the caveat of being tied to a new line so that is probably not an option. When we moved here from CA in December of 2020 our phones were old and the prepaid cards were a pain. I got 5 phones and lines just after picking up the home internet gateway. All 6 lines 210/month. I did it to get the gang all set and in January the phones will all be paid for and the kids will pay for their own lines. I know it sounds steep but was much better than other options given the terms. No contact or extra fees, unlimited data and text. The hotspots are limited but I never use my phone as a hotspot. The service has been very good and it works great for us. 

You need to see if the home internet is available in your location. If so that is a good solution for home internet and good terms. They have some specials so maybe you can get a good deal.
Go to >    T-mobile.com and check the offers and terms.  I went into a T-Mobile store and spoke with an associate when I got the family plan. I explained exactly what my objectives were and held to them and we came up with the solution. The associate was very helpful. 

From your description of how you have been careful with it and turning the gateway off it does seem excessive. With our household of 4 of us here using the internet via the gateway we pull roughly 18-20G per day. I know there have been reports from others complaining that the usage reported is not up to date so maybe they have created new problems and their system is not recording/reporting properly. 

You should check out the other conversation, Mysterious cellular data usage in early morning

Maybe you are not getting the answers you need or have not asked the right questions. Maybe your hotspot device has some similar behavior to what is reported in the other conversation. I do recommend looking into this. If the SIM is removed after the unit is powered down there should be no way for records of data consumption to take place. Review that conversation and maybe send a direct message to two_chris via selecting his avatar and doing so. Explain what gateway/hotspot you have and the behavior you are seeing and what you have done or point him to this conversation. Don't give up.