Pull switch does not turn light off?

I changed the centre light in our bathroom from one with shade to a glass one that it tight to the ceiling. I took the old one down and just swapped over the wires from the old unit to the new. Now the light won't switch off from the pull string. I tried a new pull string unit but it still does not work. I have changed nothing only the unit as the brown and blue wire were there from the old unit. There was no earth on the old unit. Coming out the ceiling is heavy duty wires Red, Black, Black and Green and these all go into a small box and the blue comes out of the Red and the Brown comes from the Black. I have changed the brown and blue around but nothing happens...Why does it not turn off ? Please can anybody help !
Thanks