Like how you aren't allowed to rent your house like hotels (AirBnB) or to use your personal car as a cab (Uber)?
I am talking about a contract that you agree to when you purchase service.
There is a significant difference between freely using something you own. vs changing how you use a service that you do not own, and have signed contracts specifying terms of use.
Even if they do, legally speaking, will you sharing the internet connection on your name with your flatmate / family members would amount to breach of contract ? In all likelihood, your flatmate shares the cost of the internet with you. Isnt this case is exactly the same, somebody else using your internet & helping you offset some of your cost. Am I missing something here ?