I used to use Mobipocket.
I suspect you are creating a toc using Word. Stop doing that, remove that toc from your document.
Instead you create the TOC within Mobipocket. Suppose your chapter headings are Heading 2 in Word. Simply put h2 on the Mobipocket toc page. If you have two levels of heading it can support that too. For example h2 on the first line and h3 on the second line.
The toc is placed right at the start, after the cover. Not ideal, but it works.
I no longer use Mobipocket but it served me well for a while. I did not enjoy having to make the ncx file by hand when a book has 30 chapters.