Congress existed under the Articles of Confederation for years before the call for the Constitutional Convention. Debates at the CC came AFTER the states were in existence so there is no surprise states were mentioned.
Congress was CHANGED to its present form by the CC but there was a Congress before ratification of the Constitution. What are you thinking of?
A Congress existed, not the Congress of the United States. The States, acting collectively and cooperatively created the Federal Government. Your assertion that the States had no part in creation of the Federal Government is patently false.