Muslims believe that the Tanakh and so-called New Testement were originally given in a form different than what they are now. Indeed, they were originally given as the Koran itself. Overtime, Muslims believe that Jews corrupted the text for their own purposes. Therefore, God sent Jesus to restore the uncorrupted text of the Koran. However, in the Islamic view, Christians also overtime corrupted the text for their own purposes. Therefore, God needed to send Muhammed as a final messanger to once again restore the pure Koran.
Accordingly, Muslims accept all Jewish and Christian prophets as prophets... but do not necessarily accept the strict text and language of their prophecies, as they feel that subsequent generations corrupted the pure original versions.
You can criticize this theology all you want, I personally find it no more unreasonable than Christian efforts to distort the Tanakh to manufacture Jesus prophecies. But your specific "contradiction" doesn't hold water.