This happened to me with our phone some years ago when my son was 15. I called the phone company, couldn't figure out what on earth happened, or why my bill was so high. Turned out my son had joined some sort of phone get together thing, a party line or something- when I told her how old he was, they immediately canceled the entire bill- since he was under 18, and this was done without my knowledge- you might check and see if they could at least reduce it because of that. They just might.
As for her complete disregard for what she has done, and the hardship it's caused you, sigh....welcome to the world of 'some teens'---I have a daughter who is now 17, who is very much like that. She does things, and doesn't really care what it does to anyone-her antics at one point caused me to lose my job, and subsequently, my home- we ended up living with friends-(calling the office constantly, to try and corner me about various places she wanted to go, and knowing that while I was at work, I wasnt going to go into an argument why she couldn't do the things she wanted to do...then hanging up on my boss when she answered the phone instead of me...sigh...we had caller ID for crying outloud)--once we were in that predicament, of living with a friend- I was blamed by her for not fixing everything and making it ok- and she was angry with me for it-and never once saw her own actions as a big contributor. Once she found out why I lost my job, it was like, 'shrug, oh, ok-'......and the demands are still there. Sigh. Talk about depressing. Like your daughter, this was always a good kid, good grades, very intelligent--and its like when she hit high school, that all changed- and none for the better.
The best thing I can tell you, and it isn't so great- is that we have to remember, our kids have their own personalities...and some of them are like this. Of course, it could be a case of rebellion that hopefully she will get over soon enough...or perhaps this is just the way she is, and she wont be getting over it. This is what has happened with me and my now 17 year old daughter- she's let up some, but not much- and she scares the daylights out of me. about all I can say, is try to hang in there- because when yours turns 18, she will be responsible for the things she does, and not you-and sadly, she will be the one who pays for her behavior. Good luck--I feel for you!