blonde colouring went too dark

Hi. My 85% grey hair has become resistant to box dyes. However, I have found a product called "Ice cream, by Inebrya" that will take. I have tried to get in touch with the company and they do not reply.
the problem is that I would like a light creamy coloured blonde, not yellowish. I have used the 10/0 Light blonde Platinum with a 20 volume. I left it on for 20 mins. It came out so dark! It is like a brown. What different colour or volume should I use to get the colour I desire?