How do I strip my hair colour of red, (which should have been blonde)back to that colour?

You need to remove the artificial pigment. This is done using ColorFix or Color Oops or, if you're in Europe, Igora Phantom. It may take more than one application of ColorFix to do the job. Here's a link to instructions for using ColorFix:

One 'n only ColorFix - Robert Craig Salon Products, Ltd.

It's possible that there may be some residual red in the hair that won't come out with ColorFix. That's not good, but bleach will get out a little of the red. What I'm saying is that you may have to bleach out the remaining red.

After all that is done, your haircolor will not be at your natural color. After all, whatever pigment contributed to your natural color is long gone. You have to figure out what color to tone it to -- preferably close to your original color but maybe lighter or darker.

Your title says "Hair and Colour loss". Does that mean that you're experience hair breakage? If so, you'll have to be very, very careful not to cause the hair to break off completely. Consider a relatively short haircut to take the weight off the hair.

If you talk to a lot of stylists, they'll say, "oh condition heavily for a few weeks and then I'll fix it". I want to warn you that hair does not heal over time. The only way to fix damaged hair is to grow it out. You can minimize the effects of damage using conditioners, and you can make the hair feel a whole lot better. But, the damaged backbone of the hair is still present and you have to remember that additional chemical services may cause it to fail (and break off).

Note also that none of this means that the hair "falls out". Hair breakage is not the same as falling out. Falling out implies to some that it won't grow back. It will grow back and it won't have to regenerate the hair below the scalp.