God is only referred to as "Father" fourteen times in the Old Testament's thirty-nine books, and even then, rather impersonally.
In those fourteen occurrences of Father, the term was always used with reference to the Nation of Israel, not to individuals. In the entire Old Testament, you will not find one individual speaking of God as Father.
Now you know how shocking it was to the Jews who heard Jesus say in the New Testament that we begin prayer with a personal relationship to God who is our "FATHER" in Heaven (Luke 11).