ALLAH CONTRADICS HIS WORD ?

Surah 6:115

The word of thy Lord doth find its fulfilment in truth and in justice: None can change His words: for He is the one who heareth and knoweth all. S. 6:115

Surah 18:27

And recite (and teach) what has been revealed to thee of the Book of thy Lord: none can change His Words, and none wilt thou find as a refuge other than Him. S. 18:27

versus 

“Do you (faithful believers) covet that they will belive in your religion in spite of the fact that a party of them (Jewish rabbis) used to hear the Word of Allaah (the Tawraat), then they used to change it knowingly after they understood it?” [al-Baqarah 2:75]

But those who were unjust changed it for a saying other than that which had been spoken to them, so We sent upon those who were unjust a pestilence from heaven, because they transgressed.(Qur'an 2:59)