Understanding Jeremiah 8:8
8 How can you say, "We are wise, for we have the law of the LORD," when actually the lying pen of the scribes has handled it falsely?
11 They dress the wound of my people as though it were not serious. "Peace, peace," they say, when there is no peace.
3 So you must obey them and do everything they tell you. But do not do what they do, for they do not practice what they preach.
Jesus would never have told the people to listen to the teachers of the Law if the very law they were teaching had not been unchanged and as pure as it was given by God. No, textual corruption was not an issue at all. It is always the question of how we react and what we do with the law that we know.
One can "handle" the word of God correctly or falsely, but there is no question that the false interpretations and preaching will affect the EXISTENCE of the word in its true form. False teaching will earn the displeasure of God, but there are others who also have the word and will speak up. Like Jeremiah in his time is sent to speak because the scribes teach lies and say that they are the true word of God. And like the true disciples in the early church against the heretics.
5 and if you do not listen to the words of my servants the prophets, whom I have sent to you again and again (though you have not listened)
6 then I will make this house like Shiloh and this city an object of cursing among all the nations of the earth.'
Obviously, God admonishes the people to obey his law which he has set before them. This would not be possible and indeed were a ridiculous command if the law were not with them so that they can indeed read and know and obey it. Both, the law of God [the Torah given through Moses], and the words brought by the many other prophets of God, like Isaiah some generations earlier and Jeremiah himself at this time.
... On the second day ... they gathered around Ezra the scribe to give attention to the words of the Law.
They found written in the Law, which the LORD had commanded through Moses, that ...
Day after day, from the first day to the last, Ezra read from the Book of the Law of God. ...
This is in about 430 B.C. about 180 years after Jeremiah's temple address which took place in 609 or 608 B.C., the first year of the reign of king Jehoiakim (see Jeremiah 26:1).
All this clearly testifies to the existence of the Law of God given through Moses at this time.