There basically isn't a way for you to do this on your own. The website owner has some issues in the site that isn't creating a good short link on the site. It is hard to know the exact link from one of these sites because they basically take your link and create a new link using their site information and a site redirect.
You'll need to contact the site owner and speak with them. Let them know you are having issues with the short links they create or the ones that have been created. This could be an issue in the site's redirect or the way they are shortening the links on the site. Unless you know how the site shortens the link there isn't much you can do about this. Basically sites short links will be a https//company name.com/xxxxxxx There is no way to correct this because you have no idea how the numbers at the end of the link work.