Categories URLs not working fine

Hi,

I’m new on this wordpress support and have tried searching wordpress for this issue but couldn’t find any solution. I’m running https://www.hindimein.com on WordPress and activated permalinks to /%category%/%postname%. Mod_rewrite is enabled but I’m facing an issue. URLs are SEO friendly but if I am opening a subcategory under category directly after sitename.com/subcategory, it is opening while it should be redirected to subcategory page under /category/subcategory or return to 404. My htaccess code is : <IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

The example of wrong another URL of subcategory can be seen at https://www.hindimein.com/mantras which is actually a subcategory of https://www.hindimein.com/astrology/ and can be accessed at https://www.hindimein.com/astrology/mantras

Please let me know how can I fix this issue.

Thanks

Vikas