Your darn right Luther and Calvin misread and mispresented Augustine. And most intelligent scholars, including the Evangelical Protestant Alister McGrath, author of Iustitia Dei, agree that they misread and misrepresented him.
Regarding the Synod of Orange, it supports the claim that Augustine taught free will and it condemns your claim that he did not. Orange II said that anyone who interprets Augustine as denying free will is wrong. That includes you. You can't even read accurately the Synod of Orange if you cite it in defense of your position.
Over against these two, Luther and Calvin, who read Augustine as having denied free will, every single theologian after Orange II and until Thomas Bradwardine in the 1300s, read Augustine as having affirmed free will. Before Orange II, there were two rival schools of Augustinian interpreters, one denying, one affirming that he taught free will to the end of his life. The controversy began already while Augustine was alive and Augustine himself told one side they were wrong--your side. Orange II then further clarified that Augustine was to be understood as defending free will. Therefore all medieval theologians, including Aquinas, interpreted Augustine's plain and explicit words defending free will as meaning exactly what they said.
Along comes Bradwardine and after him Luther and Calvin and then Jansenius and others. They were repeatedly told that they were misrepresenting Augustine. If you are going to place your trust in their interpretation of Augustine you've bet on the wrong horse because they are the decided minority view and against their interpretation stand the explicit words of Augustine.
And you've had this pointed out to you in detail again and again and again and again. You are tedious, Harley.
I would simply suggest your perception as well as your authors is tainted by your bias for your Church. If one is to read the writings objectively one would understand the arguments. It has been my experience that it’s often a mistake to rely on authors telling me what others have stated.
I started with Augustine when I heard there was a theocentric view. The statistical odds are too great that Calvin, Luther and I (as well as many great preachers throughout the centuries) could all come up with the same interpretation and look at the passages in exactly the same way. Besides, Calvin and Luther were equally adept in Greek and Hebrew. I'm confident they read Augustine in his original language just as your authors did but arrived at a completely different conclusion.
BTW-Alister McGrath is a member of the Church of England. Why would I think that he would be qualified to say that Calvin and Luther misread Augustine? Heck, I don't think half the Presbyterians and Lutherans understand the theocentric roots of their denominations and if they did they would probably deny it. There aren't many difference between Catholics, Protestants or Orthodox anymore.