Trying to get granny hair!

Hey guys,
Ive wanted grey hair since I was tiny and I've finally at 20 got round to getting it done at the hairdressers but it lasted a day!! So im just after a little advice, my hair was brown dip dyed blue (used plum by direction which went really wrong) i loved it then had to dye it the night before i started my new job, I panicked and dyed it brown over the top, unfortunately the blue had faded to a peacock greeny/blue turquoise which I loved but it stained my hair green and even after the hairdresser bleached it it was still green showing through!! Anyway I then got it toned with a grey toner at the hairdressers and it was really dark, but it faded out within a day even with silver toner shampoo and conditioner!. So I'm back to square one!! So im just after a few tips on how to get it from its current state (showed below) to a really nice shade of bright grey, I have bought color freedom permanent silver grey from Superdrug and I have two packs of bleach but I want advice before actually going ahead and making a mess of it!! Any advice would be very very appreciated! Thanks!!