Had a rift with roomate who is locking us out from internet access. Only one real ISP in my area. What can I do?

So, my fiance and I moved in with a girl she worked with back in May. Everything was going smoothly until about a month and a half ago when her ex moved back in (without talking to us or our agreeing to him moving in) Suddenly the light bill is $200 and we have gone over our internet cap to the tune of 450GB. In all, our household's usage was 800GB. Obviously, this is a ridiculous amount of usage for a household, but she doesn't have a basic understanding of any of this so we can't get that through to her.

In the end we told her that we would pay our half of the bill but not the $100 in overage charges because there is no way we used that much with what we do. Now she is going to move the router into her room and essentially lock us out from using it. She was already living her when we moved in so all services are fully in her name, which was a mistake on our end. Suddenlink and AT&T are the only ISPs in our town and AT&T shows that they do not service our particular area. We are scrambling to find some way to get our own internet service worked out.