I don't know the products you have but with a developer (oxidizing solution), this is a permanent colour.
there are a few rules to think about here:
1. permanent colour does not lighten artificial pigments... only bleach can
2. every time you put bleach or permanent colour on your hair, you damage it. EVERY time. That damage adds up. If you can avoid touching the same hair twice with permanent or bleach, you are on the right track.
3. Permanent colour, at 30 volume, will only lighten hair 2 to 3 levels. Black is level 1, medium brown is level 4, Dark blonde level 6 or 7, medium blonde is level 8, light blonde level 9 and 10.
4. If you want lightening more than 3 levels, you need bleach.
Its very difficult to know what you actually need to get the results you want without actually seeing your hair.
I would avoid using the permanent colour over top of the bleached hair again.
Have you thought of using bleach on the roots and henna over top of the rest? The colour result would be bright and shiny and a lot healthier and long lasting.
Henna does not damage and is very permanent. It covers grey extremely well.
Good luck whatever you end up doing