Question: Ezekiel 21:28-32 prophesies (in the 6th century BCE) that Ammonites will not be remembered any more. They continued to exist until the 2nd century CE. (And they are still remembered in the Bible.)
Response: The claim that the Ammonites "continued to exist until the 2nd century CE," if that is true, is not a violation of Ezekiel 21:28-32. The fact is, they no longer exist, just as the prophecy had claimed. As for being "remembered," there is an important difference between knowing that a group of people existed during ancient times and actually being able to remember any of those people.