It is extremely disappointing for me personally that some cyber-terrorist are attempting to hack my website over and over

I've transformed my FTP passwords 2-3 occasions. But nonetheless they could hack.

Cyber-terrorist can't change my all pages but when they changes my index.php using their hacking page.

Can anybody share concept that what black hole could be in code

or its problem at hosting finish?

and just how can one resolve this issue?

There is the first problem: FTP. Don't use FTP. Ever. It's naturally unsafe. Use SFTP.

However, I am confident they found a weakness in your body. Do a listing of the items you've installed and make certain you will find the latest version, and educate yourself on known problems. Just for example, I used to be using Usermin/Webmin, which in fact had known security holes... that have been quickly used.

Once you are compromised, the cyber-terrorist might use a rootkit. Individuals kits typically include duplicate versions of tools like ls and ps that hide their hacking tool. Once this is the situation, you are able to alter the password as numerous occasions as you would like - they have use of your website.

As others have recommended, you cannot provide you with better advice without more details.