A Belgian bank requiring a Belgian person to transliterate their Belgian name to English characters is somewhat similar to an Israel bank requiring to transliterate your name from Hebrew to Korean (which has as much relevance to Israel as English has for Belgium), and refusing to use Hebrew in their communication.

There are official national languages and alphabets, the involved characters are key parts of those national alphabets - who cares about what the English alphabet is? Neither the bank nor the customer are in England or in an English-speaking country, and there is a legal duty for the bank to support the national language(s).