Help! My hair is going green!

A little while ago I had my hair highlighted at the hairdressers. I had a number of streaks put in like this



As time when on i noticed that there was a slight green tinge to my hair and overtime it was getting worse. About 6m later I went back to the hairdressers to get my coloured again and i mentioned this and they said they would dye it a bit darker to try and hide/cover the green. This seemed to work but just 2 weeks later my hair was looking really green again. I had another appointment at the hairdressers and I mentioned this and they said that maybe something in the dye was reacting with.... something - I'm not sure what it could be reacting to and the hairdresser didn't seem too sure. They gave me a free bottle of clarifying shampoo and told me to use it every other wash to try to remove any build up of colour/green (I'm not sure this is actually doing anything). They said that if things didn't improve they may need to strip all the colour from my hair.

My questions are -

1) What could be causing the colour to go green? I don't swim and I was wondering if something like copper in the pipes could cause this and 2) IF they need to strip the colour do you think i'll be expected to pay for it? I mentioned the green when I had it dyed and dying it did nothing (AND it was FAR more expensive than the 1st time i had it dyed and she basically just dyed it one colour compared to before when they were highlighting it! (£100 vs £60))

it's happened to me I had ombre hair with blond tips the blond hair turned green I talked about it with a hairdresser and he explained me that the hair turned green because the other hairdresser bleach my hair too much there's no problem like copper in the pipes it's just your hairdresser who did a bad job  don't do more highlight or dye it blond it's useless the green won't go like this it's a waste of money expect if you choose a venitian blond with red pigment in it  you can go to a hairdresser and ask him to neutralize the green color with red pigment or just buy a shampoo for redhead with red pigment in it it will neutralize the green color your hair won't turn red with a shampoo blond girsl use purple or blue shampoo to neutralize the yellow or the orange color if you look at a color wheel you will understand easily purple and blue are the opposite of yellow and orange so they neutralize the color  the opposite of green is red  so if you use a shampoo for rehead  it will neutralize the color so try to just use a shampoo for redhead with red pigment and the green color will go 

@maxou - Thanks for the tip. I'll see what happens with the shampoo and then i'll try the red shampoo. Failing that i guess it's stripping the colour and hopefully the salon won't charge me!