I too seem to have the same error!!
Exception in thread "main" org.docx4j.toc.TocException: No ToC content control found
I can find this control in the document I'm working with.
<w:instrText xml:space="preserve">TOC \o "1-3" \* MERGEFORMAT</w:instrText>
However, I did not understand the solution or approach you suggested for the same.
(Sorry I'm new to working with Docx4j and Word documents as such!!)
Could you please help me here!!