Regarding your data disappearance, there are ways in which you can discover what it is that is using your data, and they are device dependent.
If you have Windows based computers, you can use Glasswire to monitor the data on the computer it's installed on. it's free, and it's here...
https://www.glasswire.com/.
If you have Apple based devices with the Apple OS, they have an app on them called the Activity Monitor, and that monitor has a Network section. This monitors data usage as well.
If you have a satellite TV receiver, especially a DirecTV receiver, it's generally advised against connecting this due to there being no way to control the amount of data it uses, even when not using its On Demand service.
Trying to figure out what is using your data can be daunting, but it needs to be done or your data will continually be used up. You can also use the above methods in a process of elimination to find the culprit.
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