my system is using my internet broadband internally. dont know which app is using its bandwidth

my system is using my internet broadband internally. dont know which app
is using its bandwidth

from few days my internet connection is got used by some application
internally by my system, 1)i want to know which application is using it?
yeah i used task manager to see which resource is using my network it just
say svchost.exe(which is internally running more services,processes cant
figured it through it) 2)can i restrict my internet access to only certain
application(i think u r gonna say firewall, i even tried it but it is
making my system damn slow, i have intel i7 with 8gb ram, so i uninstalled
it) 3)And this usage of internet making CPU usage more than 15% which
making my pc hotter. inturns makes my fan runs fast inturn makes sound.
immediatly after disconnecting my internet my CPU usage will go normal(1
or 2 % mostly even with lot of apps opend)