Ex-salon owner here.
Try to avoid colour stripping products as they will destroy the condition of the hair.
Try this instead:
Get as much as possible out using Fairy Liquid, Head & Shoulders and Vosene (alternate/experiment with each),
Rinse hair well first with warm water to warm it up and soften and open the hair follicles.
Apply the chosen option from above and work into the hair well but gently, ensure you don’t stretch or pull the hair. Don’t forget the ends.
Rinse out well using warm (but not hot) water, don’t use cool or cold water as this will close the hair follicles.
On the second application leave on, wrap hair in cling film and a towel, then add gentle heat, either from natural warmth or warm setting with hairdryer.
Leave second application on for 30 mins - 1 hour.
Rinse out well with warm water (warm not cold or hot as above).
When all is rinsed out apply a good deep conditioning treatment. This is where it would be worth investing in a good salon quality product. Work gently but well into the hair especially the ends.
Leave for 1 hour.
Rinse out well with warm water (warm not cold or hot as above). Repeat rinse with cool water.
Blot/ press dry with a towel - don’t rub or pull the wet hair.
Use a good quality leave in conditioner and comb through gentle with a wide tooth comb working from ends to roots until hair combs through easily.
AVOID drying with heat if possible and allow to dry naturally. If you mist dry with heat blot/press dry as much as possible first, apply leave in conditioner and a good heat protector product. Dry slowly and gentle with a hairdryer on the lowest setting.
AVOID using any other heated appliances especially hair straighteners as the hair will be fragile for some time and this is the most sure way of creating more damage.
Repeat the process above every 3 days (max every 2 days), anymore often will be too drying on the hair. Once you feel you’ve got out as much of the colour as possible then revert back to shampoo and conditioning 1-2 per week. At this point you can also look at possible toning options.
Colours with a purple base are more likely to neutralise orangey tonnes, Osmo super silver is good for this, you can leave it on a bit longer than it says too. Colours with a red base are more likely to neutralise green tones. An old hairdresser trick is to apply tomato ketchup to help neutralise green tones.
Look at Bleach London products. BUT ALWAYS do a strand test first before applying any kind of colour so you can be more certain of what it will come out like.
Another option is to consider a bleach bath process but I absolutely do not recommend you try doing this yourself, this needs to be done by a professional. This is also best done once you’ve got as much colour out as possible yourself through the process above.