Not everyone only few people use 2fa especially when website/company force us to do this. strong password is enough for securing our account
If he is ignoring you then you are also doing the same. How many times has he said that there is no sign message option in his wallet? but honestly he is not ignoring. language barrier and broken translators makes it difficult to understand and write many things. by the way If btc address ownership is so important don't you think we should know? It is not mentioned anywhere in the site. we would have used the official wallet not the exchange wallet.