Another cast iron question

I know, the proper method of seasoning new cast iron has been
discussed here often. But I need to repair a failed process.

I have two cast iron skillets almost older than me, and I love them,
use them often. But recently I purchased a Lodge brand cast iron
dutch oven. Love to use it. However, I went too fast. A few
concoctions evidently burned in the pan. While the metal has turned
from its initial grey into that "seasoned" black look, I suspect what
I really have is burnt carbon. Lately, anything cooked in it comes
out with a burnt taste. There is no visible "layer" of burnt residue
on the inside surface. So the burnt stuff might be ingrained into the
pan.

Does anyone know of a way to repair the damage so I can start over,
short of industrial sandblasting? I have even tried steel wool
Brillo pads, washing carefully after. Still no luck. Have I ruined
it beyond repair?

.

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