nsurlsessiond is EVIL

This is unbelievable. Yesterday, because an old PC I have which was used occasionally on a spare monitor to bring up stock quotes stopped working. This morning at 7 AM I replaced it with a Mac Mini which hadn't been used - even fired up for maybe 1 1/2 years. Now, this is why this Mac Mini and it's Mojave OS is EVIL. I'm on a metered satellite internet connection. I get 150 GB a month, which I allocate very, very carefully, usually at the rate of 3-4 gigs a day which means I usually use 120 GB max a month. I need this to conduct business as I can't even tether my cellular phone with any success here in the boonies. At 7AM this morning I check my sat net usage for the month to date: 71.0 GB. This Mac Mini was running, with NO websites or apps even open until I just shut it down. To my HORROR, right now, at 2:30 PM, 7 1/2 hours after turning on the Mac, I get a notification alert from my satellite net provider that I've hit 70% of monthly allocation!! And I'm now at 105.2 GB used. With yet another 16 days to go until that renews!! I check the usage on this Mac and it's 34.6 GIGABYTES!!! In 7 1/2 hours!! Why? Because this idiotic nsurlsessiond is listed as having consumed virtually all of that 34.6 GB of bandwidth in 7 1/2 hours! So, I've had 23% of my entire bandwidth allocation stolen from me in 7 1/2 hours to do what? To backup or send whatever it sent to the cloud and iCloud? This is insane. How do I PERMANENTLY turn this travesty OFF!! If I need something backed up to iCloud, it's ALWAYS done through my cellular plan which is truly unlimited bandwidth. I never would have even turned this Mini on if I had realized this horrible turn of events. So now I have to watch bandwidth usage so closely for the last 16 days of this month for me. Do Apple engineers not realize that people in rural areas do NOT have unlimited internet data plans? Can anyone tell me how this nsurlsessiond is totally turned off?