What you are struggling with is something a lot of individuals struggle with because of how a parent can do positive things and yet be dysfunctional. Your mother is the type of individual who doesn't admit "fault". Instead, it sounds like what your mother does is she goes on the defensive and in so doing invalidates your feelings.

You keep calling her and engaging her to get validated, and every time you do that she goes into the defensive mode. You have been stuck in confusion because she has done positive things with you in your past, yet, she refuses to validate the things she has done that hurt you in some way. It's very hard to understand how someone can love you, yet also deny you too. When this takes place it just tends to get more and more dysfunctional. This is what is happening with you and why you are stuck between shutting your mother off, yet, you don't want to disconnect entirely because she did provide "some" positives in your life.