Websites that show you the information of your internet connection such as IP, dns server etc. can detect the dns server of your ISP (independently of your operation system) if Java or Flash are enabled in your browser.
We offer the following methods to solve this problem:

1. Disable Java and Flash in your browser, but this is generally not suitable for normal internet surfing.

2. Change your dns server with one that doesn't exist. To do so you should open network settings of your ISP, then open "Internet Protocol (TCP/IP)" properties and specify the preferable DNS server as (for example) and leave the alternative DNS server empty.
After you close the VPN connection you should change the DNS settings back.

3. Change your dns server with a public one (follow the same steps as in method 2) on permanent basis.
In this case you don't need to change your DNS settings back after you close VPN connection.