The steps I did are as follows:
I created a certificate and put them in /etc/apache2/ssl/*
I created an IP / port settings with these settings:
    94.16.118.217 / 443
    unchecked: Create Listen statement
    Is this an SSL Port?: yes

In settings menu:
    SSL settings: yes
    Path to the SSL certificate: /etc/apache2/ssl/apache2.pem
    Path to the SSL Keyfile: /etc/apache2/ssl/apache2.key

    Filled all the Let's Encrypt fields

For a domain:
    DocumentRoot: /var/customers/webs/mehseyrafi/arzbin.com/
    ServerAlias value for the domain: WWW (blabla)
    SSL IP address(es): checked
    SSL redirect: checked
    Use Let's Encrypt: Checked

And restarted Apache service just in case.

Finally when I checked the website is untrusted in chrome browser and when checking the certificate, it is the certificate which I created at first step, not a certificate from Let's Encrypt.
 

So what's wrong with my steps?

On 6/16/2018 at 12:04 PM, Mehrdad said:

So what's wrong with my steps?

Nothing you are just impatient...a few minutes for the cronjob to fulfill all the tasks and a check on arzbin.com now:

Valid certificate
The connection to this site is using a valid, trusted server certificate issued by Let's Encrypt Authority X3.