You need a section break instead of a page break.

That page numbering format is using a NumPages field. That field always gives the total number of pages in a document. You could try the SectionPages field instead.

Press Alt+F9 to display field codes. Change the term numpages to sectionpages. Press F9 and the Alt+F9 again. Does that help?

This page will give you some idea of the interplay between sections and page numbering.
Numbering Front Matter (Ribbon)

For more, see Sections / Headers and Footers in Microsoft Word 2007-2013.

You could also just type the number you want instead of the field. That won't change as you add or delete pages, though.