svchost.exe is just the name for a "Service Host Process", which means that it... hosts.... Windows Services.
In other words, any number of different services may be running within an
svchost.exe instance. Some of them run only one service; other svchosts can run many different services within one svchost process.
You definitely don't want to go randomly killing
svchost processes because you may be killing useful services, like audio, networking, or your virus scanner.
Instead, what you can do is go into Control Panel, under Administrative Tools, under Services, and Stop services one at a time until the data transfer goes away.
Generally you don't want to stop services that are critical to the function of the system, and you will get warnings if you try to stop a service that other services depend upon (hint: stopping these is a pretty bad idea). BUT, you can try stopping them anyway.... here's the process:
Make sure you aren't running any programs with valuable unsaved data
Close all applications
Stop the service
If it breaks your computer, either start it again, or if you are unable to start it, simply reboot the computer and it will operate normally again (the right-click "Stop" function is only until you start it again or reboot, it isn't permanent).
Once you find THE service that is consuming the data, you can permanently disable it either by uninstalling the application it's associated with, or by going into Properties for the service (also in the right-click menu for the service), and changing the value in the drop-down box to Disabled.
P.S. -- Data caps are terrible, I feel bad for you.