Goldwell-HELP with correct color

I have coarse, thick hair that would probably be 80% gray if I didn't color it. My hair grows very fast and I have to color it every 2 weeks so I do it myself. My gray is very color resistant but the rest of my hair holds on to color and turns dark even with very light hair color.

Last year, when my daughter was getting married, I broke down and had my stylist color my hair and it came out beautiful. My natural color should be a medium to a little lighter brown with red/gold always showing through. I hate the red and it seems with hair color it ALWAYS turns brassy red. After my hairstylist colored it, it was a ashy, lighter brown with no hints of red. Loved it! The stuff she had in the bottle (Goldwell) was the green of the inside of an avocado. She knows I cannot afford to come to her for coloring but when she gave me the colors she used, I don't think they were correct. She told me to use 1/2 6NN (Dark Blonde) with 1/2 of a 7 color (can't remember which one) with 3% 10 volume developer.

The problem is my grow out is now reddish/gold and neither of those colors she told me to use were the color green she was using. The rest of my hair is no longer ashy but has reverted to the very dark brown that my previous colorist accidentally died my hair.

I want to stick with Goldwell Topchic. Should I switch to a 7NA (Mid-Natural Ash Blonde) or 6NA (Dark Natural Ash Blonde)? Also I saw that Goldwell sells something called Green Ash. What is that and when would it be used? I know that green neutralizes red which is what I need and what it seems my colorist used last year. Also, should I be using the 3% volume which she told me to use or the 6% 20 volume?

Please can someone help me. I have 3/4 inch of red/gold grow out and I would like it to be a medium ash brown.