List one category

Hello folks, I’m trying to solve the following problem:
1. List posts as post.html
2. I would like to list the categories without the word category
3. I wuuld like to list only the last category

Here is what I did to solve these issues:
1. I changed the Permalinks setting to /%postname%.html and mission accomplished
2. I used the Yoast SEO to remove the word “category” from the URL – mission accomplished
3. I installed “Single Category Permalinks” and it does shrink down the URL to the last category but I get a 404 error.

To illustrate the example. The site is http://united-states-car-exporter.com
Sample Category Listing before Single Category Permalinks: http://united-states-car-exporter.com/dealership-information/four-wheel-drive-car-dealer-exporter/4×4-left-hand-drive-dealer-exporter

Sample Category Listing after Single Category Permalinks: http://united-states-car-exporter.com/4×4-left-hand-drive-dealer-exporter

It would be beautiful if I can make this last URL work but I get a 404 error.

Most of the content has been ported over from an erstwhile Joomla site where it is listed with only the last category so a lot of links get broken when WordPress is listing the whole litany of categories. Any help would be appreciated.