Https Redirect loop

Hello, I have used many plugins to redirect urls to https but all are giving redirect loop. I installed your plugin “WordPress HTTPS (SSL)” and issue seems fixed.
But still I am having some problem. These are below:

1. By opening sitename.com/hfgfgf Then it is not going to https. Means I am opening that url which is not available so it opens 404 not found with the url http://www.sitename.com/hfgfgf But it want to open this error url also with https.
http://prntscr.com/9akrc6

2. Also I am using whmcs for billing management. WHMCS is located in public_html/biling/
I already set https url in whmcs but still not redirecting to https. Is there any method to redirect http url to https in folder “billing” ?

https://wordpress.org/plugins/wordpress-https/