How to make feedback form?

Hello, the Internet is a lot of variations of how to make a feedback form. Chose this option:
<form method="POST" id="fb" name="feedback" action>
 <span class="cls_fb"></span>
 <input type="text" name="name" placeholder="Name" pattern="[a-z]" required><br>
 <input type="tel" name="tel" placeholder="8(+7)916 775-36-01" pattern="^((8|\+7)\s\d{3}\s\d{2}\-\d{2}\-\d{3}$"><br>
 <input type="email" name="email" placeholder="Email"><br>
 <input type="submit" name="submit" value="Send">
 </form>

<?php
 if( ( isset($_POST['name'] ) && $_POST['name'] != "" ) && ( isset( $_POST['tel'] ) && $_POST['tel'] != "" ) && ( isset( $_POST['email'] ) && $_POST['email'] != "" ) && ( $_POST['submit'] ) ) {
 $to = 'exampl@exampl.exampl'. ', ';
 $to .= 'exampl2@exampl.exampl';
 $name = htmlspecialchars($_POST['name']);
 $tel = htmlspecialchars($_POST['tel']);
 $email = htmlspecialchars($_POST['email']);

 $subject = "=?utf-8?B?".base64_encode($subject)."?="."Theme";

 $message = 'Name:' . $name . "\r\n" . 'Phone:' . $tel . "\r\n" . 'Email:' . $email . "\r\n";

 $headers = "Content-type: text/html; charset=utf-8 \r\n" . 'From:' . $name . '<' . $email . '-->' . "\r\n" . 'Reply-To: NAME <exampl@exampl.exampl'>' . "\r\n" . 'X-Mailer: PHP/' . phpversion();

 mail($to, $subject, $message, $headers);
 header("Location: index.php");
exit;
 }</exampl@exampl.exampl'>

In php is not strong.
Questions:
In the $message won't work "\r\n", how to fix?
- By clicking on send, a page opens index.php if this can be removed to just send and not go anywhere?
- When the page updates, the alert window appears with resubmitting how to resubmit, KRC, how to remove this window?
How to clear the input value after submit, reset variables or js to clear the fields?
Thank you so much!
June 14th 19 at 20:59

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