This looks like mold. There isn't a way to remove mold. I have tried many method too. The only way is to dispose the clothes already.
Agree with mummy jorelle. However, I did try with using vinegar and bicarbonate. Managed to lighten it a little.
best to throw it away. or try washing it in the washing machine at 60 degrees.
Better to dispose if can. Mould can spread. :(
I soak it in alcohol before washing!
Did you try colour bleach?