If six of your chapters are missing you need to start over. If six of your chapter headings are missing, type them in again and assign them Heading Style 1.
I've noticed that Word doesn't play nicely with partial lines of title/heading formats. Make sure you format THE ENTIRE LINE OF TEXT containing the title/header, or sometimes it'll forget anything in the line is formatted at all.
(If you're doing something strange where your heaing and subheadings are on the same line - good luck. It's probably possible but tricky to do.)
Please, can anybody put me through how to format my paper into headings?
I kept on receiving "there do not appear to be any chapters in my Table of Contents and suggesting that I need to set chapter divisions." everytime I tried submitting my paper.
You can look through this article:
It has all the information about setting Heading Styles. Most basically, you need to assign Heading Styles so the EPUB converter knows what elements to include in the table of contents.