How to make php mail understand cyrillic

Question

I'm trying to make a registration from which then gets send to my email. It works with english letters but when I try typing out something in bulgarian I get this:

NEW SUBSCRIPTION REQUEST.

Company Name: п п╬п╪п©п╟п╫п╦я▐. Country: п▒я┼п╩пЁп╟я─п╦я▐. City: п▒я┐я─пЁп╟я│. Address: я┐п╩п╦я├п╟. Company Reg NO: п п╬п╪п©п╟п╫п╦я▐123. VAT: п╫п╬п╪п╣я─ 213. Liable Person: п░п╥. Contact Person: п÷п╟п╨ п╟п╥. Phone: 1234567891. Email: test@test.test. Comments, questions:nqп╪a.

I have tried the whole content-type and charset UTF-8 but I can't get it to work. Here is my php code:

<?php
if (isset($_POST['submit'])){
    $Company_Name = $_POST['Company_Name'];
    $Country = $_POST['Country'];
    $City = $_POST['City'];
    $Address = $_POST['Address'];
    $company_Reg_No = $_POST['company_Reg_No'];
    $VAT = $_POST['VAT'];
    $Liable_person = $_POST['Liable_person'];
    $Contact_Person = $_POST['Contact_Person'];
    $phone = $_POST['phone'];
    $email = $_POST['email'];
    $questions = $_POST['questions'];

    $mailTo = "myemail@...";
    $subject ="Subscription request";
    $header ="NEW SUBSCRIPTION REQUEST.\n\n";
    $companyName ="Company Name: ". $Company_Name. ".\n";
    $companyCountry ="Country: " .$Country.".\n";
    $companyCity = "City: ".$City.".\n";
    $companyAddress = "Address: " .$Address.".\n";
    $companyNumber = "Company Reg NO: " .$company_Reg_No.".\n";
    $companyVAT = "VAT: ".$VAT.".\n";
    $companyLia = "Liable Person: ".$Liable_person.".\n";
    $companyContact = "Contact Person: ".$Contact_Person.".\n";
    $companyPhone = "Phone: ".$phone.".\n";
    $companyEmail = "Email: ".$email.".\n";
    $companyQuestion = "Comments, questions:".$questions.".\n";
    $message = $header. $companyName.  
        $companyCountry. $companyCity. $companyAddress. 
        $companyNumber. $companyVAT. $companyLia. $companyContact.
        $companyPhone. $companyEmail. $companyQuestion;
    $mailHeaders='From:TestMail';

    mail(   $mailTo,
            $subject,
            $message,
            $mailHeaders);
    header("Location: success.html?mailsend");   
     
}
?>

This file is being triggered by a post form with a submit button. You can see its fields at the top of the code, it's nothing special.