Did you paste your entire htaccess file into the tester or just the page redirects? I wonder if you have an error in another part of the htaccess file that’s causing it to fail. I think Doug asked you to post your complete htaccess file, and I don’t recall seeing it posted.
If you pasted your entire htaccess file into the tester for your tests, then the issue has to be with your hosting provider. Showing them that the tester confirms the htaccess rules are correct and are not on your site should be enough to convince them the problem is in the hosting side of things.
If you did not past the entire htaccess file and only the page redirect section, then I would try the tested again with the full htaccess file.