Data not stored in database

I'm having trouble finding the error here. I'm receiving data through the following html form:

<form action="insertpacient.php" method="POST">
<br> Prenume:
<br>
<textarea name="firstname" required></textarea>
<br>
<br> Nume:
<br>
<textarea name="lastname" required></textarea>
<br>
<br> Sex:
<br>
<select name="sex" size="1" required>
<option value="" selected hidden>Selectați o variantă</option>
<option value="Feminin">Feminin</option>
<option value="Masculin">Masculin</option>
</select>
<br>
<br> CNP:
<br>
<textarea name="cnp" required></textarea>
<br>
<br> Număr de telefon:
<br>
<textarea name="phonenumber" required></textarea>
<br>
<br> E-mail:
<br>
<textarea name="email" required></textarea>
<br>
<br> Adresă:
<br>
<textarea name="address" style="height:100px;" required></textarea>
<br>
<br> Discount:
<br>
<select name="producername" size="1" required>
<option value="" selected hidden>Selectați o variantă</option>
<option value="5">5%</option>
<option value="10">10%</option>
<option value="15">15%</option>
</select>
<br>
<br>
<input style="width:40%;background-color:#F4FDFE;border-radius: 5px; border:2px outset #FFFFFF; height:24px" type="submit" value="Submit">
</form>

And this is the insertpacient.php file:

<?php
$firstname   = $_POST['firstname'];
$lastname    = $_POST['lastname'];
$phonenumber = $_POST['phonenumber'];
$cnp         = $_POST['cnp'];
$address     = $_POST['address'];
$email       = $_POST['email'];
$discount    = $_POST['discount'];
$sex         = $_POST['sex'];
if (!empty($firstname) || !empty($lastname) || $sex == 'Selectați o variantă' || $discount == 'Selectați o variantă' || !empty($phonenumber) || !empty($cnp) || !empty($address) || !empty($email)) {
$host       = "localhost";
$dbUsername = "root";
$dbPassword = "";
$dbname     = "pharmagest";
$conn = new mysqli($host, $dbUsername, $dbPassword, $dbname);
if (mysqli_connect_error()) {
die('Connect Error(' . mysqli_connect_errno() . ')' . mysqli_connect_error());
} else {
$SELECT = "SELECT lastname From pacients Where lastname = ? Limit 1";
$INSERT = "INSERT Into pacients (firstname,lastname,phonenumber,cnp,address,email,discount,sex) values(?,?,?,?,?,?,?,?)";
$stmt = $conn->prepare($SELECT);
$stmt->bind_param("s", $lastname);
$stmt->execute();
$stmt->bind_result($lastname);
$stmt->store_result();
$rnum = $stmt->num_rows;
if ($rnum == 0) {
$stmt->close();
$stmt = $conn->prepare($INSERT);
$stmt->bind_param("ssddssds", $firstname, $lastname, $phonenumber, $cnp, $address, $email, $discount, $sex);
$stmt->execute();
header("Location: insertpacientconfirmationpage.php");
} else {
echo "NAH";
}
$stmt->close();
$conn->close();
}
} else {
echo 'ERROR';
die();
}
?>

It does go to the confirmation page, but data is not stored in the database, for some reason.

I have to mention i have used the very same code for gathering data for another table, but I had to change some input types.

Thank you in advance.

Problem 1: You're sending the discount ($_POST['discount']) with the name producername. So, it should be $_POST['producername'].

Problem 2: Your first query is unnecessary since you can make the lastname unique or some other columns like email or phonenumber.

Problem 3: You should be using && instead of || in your if statement. Or you can refactor nested if statements (arrow type code).

<?php
$firstname   = $_POST['firstname'];
$lastname    = $_POST['lastname'];
$phonenumber = $_POST['phonenumber'];
$cnp         = $_POST['cnp'];
$address     = $_POST['address'];
$email       = $_POST['email'];
$discount    = $_POST['producername'];
$sex         = $_POST['sex'];
if (empty($firstname) || empty($lastname) || $sex == 'Selectați o variantă' || $discount == 'Selectați o variantă' || empty($phonenumber) || empty($cnp) || empty($address) || empty($email)) {
die('Error');
}
$host       = 'localhost';
$dbUsername = 'root';
$dbPassword = '';
$dbname     = 'test';
$conn = new mysqli($host, $dbUsername, $dbPassword, $dbname);
if ($conn->connect_error) {
die('Connect Error(' . mysqli_connect_errno() . ')' . mysqli_connect_error());
}
$INSERT = 'INSERT INTO pacients (firstname, lastname, phonenumber, cnp, address, email, discount, sex) VALUES (?, ?, ?, ?, ?, ?, ?, ?)';
$stmt = $conn->prepare($INSERT);
if ($stmt->bind_param("ssddssds", $firstname, $lastname, $phonenumber, $cnp, $address, $email, $discount, $sex) && $stmt->execute()) {
$stmt->close();
$conn->close();
header('Location: insertpacientconfirmationpage.php');
}