I have a few ideas as to why your hair has changed from an ash tone to red tone.
Is it possible that you went to a lighter brown shade even though you dyed your hair an ash tone?
The lighter colour can cause a chemical to an oranginess - and the ash neutralized it to a reddish colour.
Always check the mixer tube in the box before you purchase it - sometimes people like to play games and switch colours. Almost happened to me if I hadn't looked.
I have been dying my hair for countless years. The one thing I do notice is how easy the dyes want to come out red/gold/brassy even if they say they are neutral or even ash tones.
Dark brown hair can have red/auburn/golden tones. Sometimes hard to tell because it is dark.
Even if you use an ash shade, once if fades, the natural tones can can through again.
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If you want to get rid of the red tones and get the ash back, the bast bet is to go to a decent salon and have a colourist do it. If you try to do it again at home, you still might have problems and you'll just end up drying your hair out.