I have naturally long, very light blonde hair and decided to try a non-permanent black hair dye which apparently lasts 28 washes as it would then wash out without permanently changing the colour of my hair.
However I've washed my hair a good 30-40 times since doing it and the colour hasn't even faded in the slightest and there is no sign of any colour washing out my hair whenever I wash it. I only wanted to try black hair for the month it said on the box just for fun but I'm worried it's never going to come out now!
When I applied the dye I did leave it on slightly longer than it suggested because the hot water ran out in my house and I had to wait a short while for it to heat up so maybe this is what's pro-longing it?
Do you have any advise on how I can get my naturally blonde hair back fast?! Or am I stuck with it until it grows out?

Well, on the box it should have said that its not suggested on grey or very light hair, it's kind of like how stains are harder to get out of white clothes than say, dark purple clothes.

You should wash it for another week or 2 and if it doesn't fade, go to a salon and as them to take the color out for you.

A semi-permanent color can last longer on blonde hair or chemically treated hair. But if your hair is porous and you use a dark/black color, this may absorb the color and leave a permanent tint on your hair. You will need to strip the color from your hair and then apply a blonde toner that's close to your natural hair color. It would be best to have it professionally done.

Thanks for the advice, I will give it a try!