GS,
I so feel for you. You have described my years with my mother (the insatiable calls, demands for attention that never "feeds" or assuages her because one bit of attention leads to a bottomless list of demands for more). To a T.
I'll tell you when it changed. One night, when she was calling/calling/calling...I tried a different tack, which was to approach her from her OWN reality (that she doesn't get enough attention).
I went and sat with her and said, with sympathy:
You know, you are right. You deserve so much more time and attention than I am able to give you. I know it's not enough, and you really deserve much more. But I've come to realize that I just can't do it. I simply can't give you all the attention you deserve. And I'm sorry. But it's the truth. I love you, and I'm going upstairs now.
She was briefly silenced. I had to repeat it a few times, but over months, something sank in, because for the first time in my life, she behaved as though she expected somewhat less.
Hope that might help you, GS.
It was a startling change. I just "entered her world" and addressed her needs from inside that view.
love,
Hops