Parent Refusing To Pay Phone Bill That Is In My Name

I have a greedy mother who I have distanced myself away from. In 2017 when we were on much better terms I put her on my phone bill account. She would just deduct the bill from the monthly rent she had me pay her. A few years later I moved out.

In 2020 I switched phone carriers so it’s just her on the account. Over the years she has become self destructive and has become substance abuser (alcohol, pills, and so on). She refuses to pay the bill that is now $300. I told her this and sent her a link to change account responsibility to her name, she still refuses. I don’t want her ruining my credit now being held responsible for her actions. What can I do to get out of this situation?

I currently live pay check to paycheck and can’t afford her bill if it comes down to that.