Brake noise is almost never just caused by adjustment. You probably have something else going on.

have the shoes recently been replaced? Did you have the drums turned? Did whoever turned them "cut back" the ridge inside?

As others have said, grease, oil, etc on the lining is a big cause. Also, new shoes DO take some time to seat. It might be helpful, if these are new shoes, to have them "arced" IF you can still find anyone with an arcing machine