3.In which instances, as described in the Old Testament, did God speak "by angels"?

Under the old covenant the Word of God often came through angels: to Abraham, to Lot and his family, to Moses and Israel in the wilderness, to Joshua, to Gideon, to David, to Daniel. If that word was disobeyed, as in the case of the instructions given by the angel to the family of Lot, there was swift punishment.