Special characters may not be displayed correctly in your mysql data base when you pass php string to mysql statement.
https://github.com/phpmyadmin/phpmyadmin/wiki/Garbled_data
First thing you should do is to make sure that your mysql database encoding is set to utf-8. You can easily do that through phpmyadmin.
Then make sure the string you send are properly encoded in UTF-8 by using the php function http://php.net/manual/en/function.mb-convert-encoding.php
string mb_convert_encoding ( string $str , string $to_encoding [, mixed $from_encoding = mb_internal_encoding() ] )
Example:
$name=mb_convert_encoding($response,"UTF-8");
Lastly make sure that the first query you send to you databse is SET NAMES utf8 like in the example below:
$con=mysqli_connect("localhost","my_user","my_password","my_db");
$con->query("SET NAMES utf8");