Well, there is only One True God. Angels are created beings, not God. Michael was a created being.
Jude 1:9
But when the archangel Michael, contending with the devil, was disputing about the body of Moses, he did not presume to pronounce a blasphemous judgment, but said, “The Lord rebuke you.”
You've never heard of our Lord being referred to as an angel?
Genesis 22:11-12
11 And the
angel of the Lord called unto him out of heaven, and said, Abraham, Abraham: and he said, Here am I.
12 And he said, Lay not thine hand upon the lad, neither do thou any thing unto him: for now I know that thou fearest God, seeing thou hast not withheld thy son, thine only son from me.
Genesis 22:15-18
15 And the
angel of the Lord called unto Abraham out of heaven the second time,
16 And said, By myself have I sworn, saith the Lord, for because thou hast done this thing, and hast not withheld thy son, thine only son:
17 That in blessing I will bless thee, and in multiplying I will multiply thy seed as the stars of the heaven, and as the sand which is upon the sea shore; and thy seed shall possess the gate of his enemies;
18 And in thy seed shall all the nations of the earth be blessed; because thou hast obeyed my voice.
Exodus 3:2-4
2 And the
angel of the Lord appeared unto him in a flame of fire out of the midst of a bush: and he looked, and, behold, the bush burned with fire, and the bush was not consumed.
3 And Moses said, I will now turn aside, and see this great sight, why the bush is not burnt.
4 And when the Lord saw that he turned aside to see, God called unto him out of the midst of the bush, and said, Moses, Moses. And he said, Here am I.
Read all of Judges chapter 6...
Actually, it is so prevelent in the Bible that the Lord is called an angel of the Lord, I'm surprised people don't know this.