Problems with contact form and input validation - php

Question

Ok so I am trying to create a contact form that validates user input to keep hackers from submitting codes and trying to require number, text, and email only. I have already styled the form and imported my php file. The contact from will send it to my gmail account. but everytime I test the php It allows for any type of data to be entered no matter if it is supposed to be a number and letters are submitted and the other way around. If I could get some help in telling me where I went wrong that would be great. I am a beginner at programming and only have the knowledge I recieved from school but I'm pretty good at html and css but having problems with the php validation. The form sends the email but like I said it allows any and all input.
<?php
$name = $_POST['name'];
$tel = $_POST['tel'];
$email = $_POST['email'];
$message = $_POST['message'];
$from = 'From: www.webdesignheros.com';
$to = 'heenanwrk#gmail.com';
$subject = 'Service Email for HeenanTech';
$tel = filter_input(INPUT_POST, 'tel', FILTER_SANITIZE_INT);
$name = filter_input(INPUT_POST, 'name', FILTER_SANITIZE_STRING|FILTER_FLAG_NO_ENCODE_QUOTES);
$email = filter_input(INPUT_POST, 'email', FILTER_VALIDATE_EMAIL);
$message = filter_input(INPUT_POST, 'message', FILTER_SANITIZE_STRING|FILTER_FLAG_NO_ENCODE_QUOTES);
$body = "From: $name\n Phone: $tel\n Email: $email\n Message: $message\n";
?>
<?php
if ($_POST['submit']){
if(mail($to, $subject, $body, $from)){
echo'<p>Thank you for your email!</p>';
} else {
echo '<p> Oops! Something went wrong, try sending your message again</p>';
}
}
?>
Additionally the form can be found at [http://webdesignheros.com/Contact.html][1]
[1]: http://webdesignheros.com/Contact.html and if someone could tell me how to reject certain input before the submit that would be awesome too. like if an invalid entry was input and they move on to the next input it would reject it and not let the submit button be pushed. would i use the pattern="a-z" in the html or would i need to add javascript for that?

Answer 1

<?php
if (isset($_POST["submit")){
$name = $_POST["name"];
$tel = $_POST["tel"];
$email = $_POST["email"];
$message = $_POST["message"];
$from = "From: www.webdesignheros.com";
$to = "heenanwrk#gmail.com";
$subject = "Service Email for HeenanTech";
$body = "From: $name\n Phone: $tel\n Email: $email\n Message: $message\n";
mail($to, $subject, $body, $from);
if(mail($to, $subject, $body, $from)){
echo'<p>Thank you for your email!</p>';
} else {
echo '<p> Oops! Something went wrong, try sending your message again</p>';
}
}
?>