Please help. I literally feel like I am about to lose my mind. This is regarding dealing with a family member?

that is a pathological liar. I have gotten to where i cringe when the phone rings and it is her. The more I do not answer, the more she call. Daily now. Without going on and on I will say that she constantly makes up serious conditions about her health. She makes up all the tests she is having done. She forgets the lies she tells me as she calls my mom and gives her a different surgery that she is going to have for the same day. It is sick. If it is not about this, it is all the drama with her and her husband. She is constantly calling and crying that she is leaving him. That he has done one cruel thing after another to her. Truth is they both stay on drugs and drunk. My sister has lied like this all of her life. I know if I confront her all she will do is start crying and denying all of it and go on and on about poor me. I know that I have to cut all ties now, i just do not know how. What can i do short of blocking my number from her. Also, once I do break contact, she will start bothering my 75 year old mother and asking about me. How do I deal with this. Please please give me advise.