I asked for “empty”, but the page is numbered

If you use \pagestyle{empty} and you find some pages are numbered anyway, you are probably encountering one of the style decisions built into the standard LaTeX classes: that certain special pages should always appear with \pagestyle{plain}, with a page number at the centre of the page foot. The special pages in question are those (in article class) containing a \maketitle, or (in book and report classes) \chapter or \part commands.

The simple solution is to reissue the page style after the command, with effect for a single page, as, for example (in article):

or (in book or report)
\chapter{foo bar}
A similar technique doesn’t work for a book or report \part command pages. For that, and for other detail, take look at “getting rid of page numbers”.