Just looking at the textual evidence it seems first mention of Judas being a devil is in John 6 which would make it in or near Jerusalem the end of his second year of ministry, the Passover before his last. John 12 and Luke 22 are first mention of his having been a thief, so I assume Judas made his decision at the time of John 6. Judas was one of Messiah's chosen Apostles. He called him and he responded, but he did not persevere and he chose to betray him. I see free will involved here. Of course I could be wrong, and we will find out.
You're wrong for a couple of reasons. First, in making the assumption. And, secondly, in the wording of the verse:
But there are some of you who do not believe." (For Jesus knew from the beginning who those were who did not believe, and who it was who would betray him.) And he said, "This is why I told you that no one can come to me unless it is granted him by the Father." (Joh 6:64-65)
Christ was speaking to people who had heretofore followed Him:
Joh 6:66 After this many of his disciples turned back and no longer walked with him.
But He does not speak of them as having received it from the Father to believe, and then of rejecting. His reply to them is that He knew their unbelief, telling them so, and then saying "That is why I told you that no one can come to me... etc". Their faithlessness in His message is explained by that statement, which puts their unbelief not on a failure in God's "granting" or "giving" or saving, but in the lack of it.