"God knew they wouldnt repent so God knew He wouldn't repent."
So, God goes around saying things He doesn't mean?
False.
There's a principle you need to take a look at:
Jeremiah 18
6 O house of Israel, cannot I do with you as this potter? saith the LORD. Behold, as the clay is in the potter's hand, so are ye in mine hand, O house of Israel.
7 At what instant I shall speak concerning a nation, and concerning a kingdom, to pluck up, and to pull down, and to destroy it;
8 If that nation, against whom I have pronounced, turn from their evil, I will repent of the evil that I thought to do unto them.
9 And at what instant I shall speak concerning a nation, and concerning a kingdom, to build and to plant it;
10 If it do evil in my sight, that it obey not my voice, then I will repent of the good, wherewith I said I would benefit them.
The people already knew of their faith from Micah in the days of Hezekiah. I think it's safe to assume Jeremiah knew it as well. God doesn't go around saying things He doesn't mean. Your interpretation is flawed. I can't help it if you can't read the text.