As an interesting aside HSBC is not an acronym, it an initialism, acronyms can only be an acronym if they are pronounceable. NASA is an acronym HSBC isn't.
So. Christmas was always called Christmas. In the 18th century the first letter for the Greek word for Christ which looks like a capital X (Chi, pronounced Kai as in chi-squared the stats test also written X2) is put before -mas (Latin for Mass) for a shortened way of writing Christmas. The pronunciation never changed to ex-mas.
Since which some people started mistakenly calling it ex-mas when it was never actually meant to be said in that way. But, that's now popular language. So. Its originally said Christmas, but more recently its read Xmas although there is the odd Brillomaster out there who says it how it is