How to go from light (bleached) blonde back to level 7 ash blonde without it washing out in a month?!

Like the title says, I have natural 7 ashy blonde hair. I’ve been getting it bleached lighter for years. I’m wanting to just be all over natural again. I went in December & got it done. Looked perfect but had done turned back bleached blonde by February. Went back in February and same thing, color had all washed out but this month.

I asked my hairdresser if there was something more permanent then just toning it, as in can we just dye it a she said no.

Is that right or should I find another hair dresser?