[OMFG!You'reActuallySmart!]

In my view you're both to blame for this issue although for different reasons. You're to blame by continuously giving stuff to her and putting up no resistance as though you were her own personal convenience store. Helping out a friend complete an assignment is perfectly fine and giving them answers when they were in a bind is understandable. She is certainly to blame for treating you like a convenience store and being rather harsh in her responses given all the stuff you did for her. There is no doubt in my mind she is using you.

The only way to stop it is for you to put your foot down. When she asks for something, the answer is automatically no. If she asks why, then tell her truth: the friendship ended a while ago and she has been dragging you along, treating you like dirt and making you feel miserable. Even if she apologizes, it's a joke to think one petty, "I'm sorry" can make up for her actions no matter how sincere. If you have to do a group assignment, don't include her. If she asks for your phone, tell her to ask someone else or get her own phone. There is nothing left to salvage, she is at fault for demanding everything then treating you like crap. The important thing for you is to learn for the future, when your friend begins to demand stuff time and time again, don't give in.