I'm not seeing this problem or not understanding your issue.

The reason a 'last line' on a page is the last line is that there is no more space on the page. If you then take away some of the space with a footnote then there is now even less space and that 'last line' HAS to move to the next page. The footnote and its reference will both appear on the Next page. If you reduce the content above the referenced paragraph such that there is space on the preceding page for both then both can move back onto the original page.

Are you seeing the footnote and its reference being displayed on different pages to each other?

__________________
Andrew Lockton
Chrysalis Design, Melbourne Australia