“I tell them never to say Ameen after Surah Fatiha because it violates the Prophet's Sunnah. I am immediately declared a Kafir…”
Sir, this is a usual chronic blow of exchange among Muslims when they are deaf and dumb. Just look how aptly this works:
What can be asserted without Quran can equally be dismissed without Quran.
Ameen is an affirmation of Surah Fatiha in conduct only what the Quran prescribes for all. Whether utter the word loudly or do not utter it at all, Quran doesn’t worry about it.