Chapter numbers / titles in ToC

Hello forum,

I'm converting a .docx document into ePub. In the original Word doc, chapter headings consist of a chapter number followed by a chapter title, with a line break in between. For example, a new chapter might start:

"Chapter 1
Title of New Chapter"

I'm using a Heading 2 style for all these chapter headings. When I convert the ebook to ePub, then the Table of Contents contains two entries for each chapter: the chapter number and the chapter title. How can I make these chapter headings a single item in the ToC while keeping the format of "chapter number /line_break/ chapter title?"

Many thanks,

T