Word's numbering feature has never worked intuitively. The buttons for numbering work fine if you are going to have one numbered list.

Using the hunt and peck method of using Word numbering results in "spaghetti numbering." That's a technical term.

To have numbering work well, you need to tie it to styles.
How to create numbered headings or outline numbering in Ribbon Versions of Word by Shauna Kelly

To be able to do that, you really have to spend time learning Word.
The following is for Windows, not the Mac. Nevertheless, it should be helpful:
Basic Concepts of Microsoft Word - from Shauna Kelly
That is a series of web pages. I recommend highly that you step through them all. You will recover the time you spend doing that within a week of using Word. It may save you from tearing your hair out.

You can find more on Word's numbering and how to make it work here: Numbering in Microsoft Word
That is my page. However, when I want to make numbering work, I go to the Shauna Kelly link as a Bible.