Hi Gampsy I'm so sorry for your situation, my mother is the same but only to me so I am estranged.
If you want to estrange her I feel you have every right. You've tried to reason, you've tried to be there for you and she makes it clear to you it's not good enough and she doesn't care.
There is another method you can try though. It didn't work for me because others around me did not see that side of my mother but it could work well for you and does for others I know.
It is called Grey Rock.
You give your mum no personal information so that she cannot use it against you. This protects you from hurtful remarks about you or other family members issues and it gives her no satisfaction from hurting you.
You keep conversation polite, talk about her, talk about the weather, talk about the garden or a bird you saw... Just inane chatter. Also set time limits for calls and visits, for you not her. Knowing when you are leaving the situation allows you to do so more easily.
You ignore anything hurtful she says and if she tries to say anything hurtful, you just end the conversation by making a polite excuse and putting the phone down or leaving the room. You do not ask her to justify herself or try to reason with her, instead you do not give her an audience for it. You just have no reaction but to not give her attention for it.
Basically you become as boring as possible so she can get nothing out of verbally abusing you, making unfair comparisons or any of her other techniques to hurt you.
With yourself fully in control this can make it possible to stay in contact with a person like this while gaining strength, confidence and healing yourself.
That's just a suggestion though, if you wish to go no contact with her for your own peace that's exactly what you should do.