The Greek word twice translated ‘accursed‘ is anathema. It was used in the Greek Old Testament for the divine ban, the curse of God resting upon anything or anyone devoted by Him to destruction. The story of Achan provides an example of this. God said that the spoil of the Canaanites was under His ban-it was devoted to destruction. But Achan stole and kept for himself what should have been destroyed.
So the apostle Paul desires that these false teachers should come under the divine ban, curse or anathema. - P24