I have just revised my blogs on keeping internet costs down with narrow expensive connections. Its still rather longwinded, so here is a summary!
All gadget providers now believe that every one has unfettered access to broadband. Alas there was still part of the world where that is expensive or does not exist, and those of us forced to use Satellite communications from the field have big problems. The costs are so high an update would break the bank. We cannot control what out phones and PCs do in the background.
My solution was to make sure that anything I plugged into the satellite device/route never knows the route to the internet. I set them so that there was only one route in the IP tables, the route via the satellite to a proxy server. Then I used another browsers such as Opera or Sea Monkey as they have email clients. These browsers can set their own connections via a proxy server independent of the operating system, so nothing else can connect to the internet.
This is detailed on https://bulger.co.uk/satellitecost.htm
other ideas to reduce costs on satellite are here https://bulger.co.uk/satellitecost2.htm