Toner made hair a gross grey/brown.

I naturally have very dark brown hair and it has taken me a year and hundreds (if not thousands) of dollars to get to a beautiful platinum blonde/white colour. I only just recently got it done 4 weeks ago and returned to the hair dresser this afternoon for a touch up before I head overseas on a holiday this weekend. I told her I wanted it lighter or the yellow tinges lifted. She for some unknown reason chose to put a dark ashy toner through my hair. This has turned the whole top of my hair brown and has made the ends this gross grey colour which I absolutely hate! How do I get rid of this? How do I wash out this toner and get my beautiful white hair back? I've only had my lovely white colour for under a month and now it is destroyed.