header location not working in my php code

That is because you have an output:

?>
<?php

results in blank line output.

header() must be called before any actual output is sent, either by normal HTML tags, blank lines in a file, or from PHP

Combine all your PHP codes and make sure you don’t have any spaces at the beginning of the file.

also after header('location: index.php'); add exit(); if you have any other scripts bellow.

Also move your redirect header after the last if.

If there is content, then you can also redirect by injecting javascript:

<?php
    echo "<script>window.location.href='target.php';</script>";
    exit;
?>