Your site is hosted on windows server right? so .htaccsess will not work, because it work with Apache server, on windows server you have to use IIS server, so you need web.config.
i am already doing URL rewrite on windows server with core PHP,
try this web.config
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
<system.webServer>
<rewrite>
<rules>
<rule name="Imported Rule 1" stopProcessing="true">
<match url="^.*$" />
<conditions logicalGrouping="MatchAny">
<add input="{REQUEST_FILENAME}" matchType="IsFile" />
<add input="{REQUEST_FILENAME}" matchType="IsDirectory" />
</conditions>
<action type="None" />
</rule>
<rule name="Imported Rule 2" stopProcessing="true">
<match url="^.*$" />
<action type="Rewrite" url="index.php" />
</rule>
</rules>
</rewrite>
</system.webServer>
</configuration>