即使不应该，MySQL INSERT INTO也会更新

My problem is that with a specific table in my database even if I use a simple INSERT INTO query the data gets updated instead of giving me a "Duplicate" error if the primary key already exists.

Structure of the table:

user_id (PRIMARY_KEY) | email (VARCHAR) | token (VARCHAR) | created (DATETIME)

If I excecute this:

$sql = "INSERT INTO
            email_confirmation (
                user_id,
                email,
                token,
                created
            ) VALUES (
                :user_id,
                :email,
                :token,
                NOW()
            )";
$query = $this->connection->prepare($sql);

$values = [
    ':user_id' => $customer['id'],
    ':email' => $customer['email'],
    ':token' => $token
];

$query->execute($values);

It will update my row instead of giving me an error if primary key already exists. Can anyone explain me why is this happening?