Two Tone Hair "HELP" - color advice

I am new around here and was looking for some color advice for my two tone hair color. here is the situation-
my natural hair color is medium brown. i have curly hair. i have been dying my hair an auburn color for a while but stopped using the auburn color back in october. a few weeks ago i used feria golden brown and the roots lightened up, but the bottom part of my hair did not, so my hair does not match and is two toned. a hair stylist friend recommened using a product by loreal called effalox to removed the auburn from the bottom hair. i am so afraid of damage to my hair as i have experienced that before. if anyone has every used the product or make a recommedation to get my entire hair a golden brown with minimal damage i would really appreciated it. thanks so much