Colour help - blonde hair gone blue

We need a lot more detail.

What did you use?

What was the colour before you used it and what was the history before that?
And anything else that might help.

Schwartzkopf colour xxl 02 atomic blonde,  and I had the same one on my hair which I died in mid January I've always used the same one every 3-4 months as I have short hair so the roots are obvious by then, I left it in for 30 mins not 45 like the dye said you can as I noticed it was looking slightly blue which it never has before. And now I don't know how to fix it, the roots have gone an orangey blonde and the rest has gone a pale/pastel kind of grey blue colour

Oh, I know that hair dye pretty well, since a lot of my friends tried that same product. Every single one of them ended up disappointed, so I did a little research for them, because there's no way so many people would complain at the same problem, if it's supposed to work according to the description. I thought they might be doing something wrong, so I carefully investigated the product. 02 Atomic Blonde is not just a typical hair dye, the box says that it has a lightening effect up to 4 levels. It might turn brown hair ginger. As to why it turned blue, might be some chemical reaction, as the box says: DO NOT use on previously dyed hair.
You might have done something wrong just like a lot of my friends. I would suggest initially using other product. Since this colour has a bleaching effect anyway, you should have bleached your hair from the start and applied any other blonde dye. If your hair hasaleady been bleached really well, you could have just applied some other hair dye, the one without lightening effect.
Hope this helps.

It is basically just bleach.
Your roots are orangey because it didn't lighten them enough.
Did you have any toner at all in the lengths? They can go blue/green when bleached.
You need to lighten the roots further to get to blonde, a strong shampoo should help to fade the blue tones., if the run off from the bleach doesn't take it out.