I'm going to cut the internet off for a flatmate
Why do you think you need to cut him off?
Yes, he berates me for being on all the time, but so is he.
Yes, that can be annoying, but cutting off their internet won't help, especially if he really needs it. You should probably ignore them, or find a new flat if that's not possible.
I'll just do it, it's ok.
If someone pays for utilities you can't cut them off. The internet is very important for people and might even effect his job. You should just find a new roommate.