Webservice method getting null parameters

When I call my webmethod from browser it runs okay and gives results, but when called from NAV 2017 all passed arguments are null. This is the xml http request I generate from NAV:

<?xml version="1.0"?>
<soap:Envelope xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<soap:Body>
<BarcodePrintZpl>
<user>testuser</user>
<variablesString>testvars</variablesString>
<filepath>testfile</filepath>
<printerName>testprinter</printerName>
</BarcodePrintZpl>
</soap:Body>
</soap:Envelope>

And that's the request in browser, which works:

<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Body>
    <BarcodePrintZpl xmlns="http://tempuri.org/">
      <user>string</user>
      <variablesString>string</variablesString>
      <filepath>string</filepath>
      <printerName>string</printerName>
    </BarcodePrintZpl>
  </soap:Body>
</soap:Envelope>

I think it could be related to namespaces of child elements inside BarcodePrintZpl . If I set the namespace for BarcodePrintZpl then all child nodes get some default empty namespace. When I try to remove the default namespace with removeAttribute('xmlns') it's still there. Can you help me?