It isn’t free, but I use a seedbox for running my Plex server. That way none of the media downloading is done on our local internet, all the ISP should see is that we are streaming data from a Plex server. They’d have no knowledge on if we own that data or not. I’m sure Jellyfin can also easily be run from a seedbox

Having a seedbox is also helpful because our internet has a pretty low upload speed, which would make watching anything outside the house a massive pain.