Toss em and buy synthetic? Seriously, are you sure that it isn’t dead and you are seeing the leftovers? You hit it pretty hard.
I guess the next thing would be to boil them, 20 minutes at 100C is supposed to kill most anything. The problems with molds is they grow from spores that can be really tough. Oak is porus, so spores could hide easily. Did it spread to the bungholes? Or just on the outside. I have seen bungs in Europe covered in mold on the outside, wet cellars. Didn’t seem to worry anyone.
Sorry, mostly random thoughts.