Hello,
I have had very blonde hair all my life and yesterday had the hair dresser match a colour to what was my natural hair colour except the colour has come out twice as dark!
I now had darkish brown hair when I only wanted dark blonde..
Do you think it might be able to tone it out? He said it was a semi permentent
I just don't want to go back to him again!
Please help!

I am unsure about the purple toner as I believe this usually works to remove brassy tones from blonde hair, but I have found from personal experience that cheap supermarket shampoos (excluding colour stay of course) such as Herbal Essences or even Baby shampoo will help remove some of the colour. Wash, rinse and repeat a few times and you will achieve your desired result in less than no time :)

Violet adds to yellow to make it look whiter. It doesn't actually lighten the hair.

If you want to fade your hair, use a clarifying shampoo or (worst case) something like ColorFix (a haircolor remover).

Semi-permanent haircoloring used on bleached hair is often absolutely permanent -- often more permanent than "permanent" color. If that's your problem, you'll have to use ColorFix or Color Oops or Color Zap (Color Zap is a bleach).