Garner Nutrisse hair colour did not work

I bought two boxes of Garnier Nutrisse creme dark golden blonde 7.3 because I have long hair and my hair is dark brown with blonde highlights but the colour did not make my hair lighter. I left it on for an hour and I'm very disappointed. I wouldn't have bought it if it wasn't appropriate for dark hair but because the box shows it's suitable for darkest brown to black hair. So why didn't it work.