SOAP and PHP. How do I retrieve this response?

I am stuck on a problem for a while now. I'm trying to get this request, that works in SOAP UI, to work in PHP:

<soapenv:Envelope xmlns:soapenv="http://ift.tt/sVJIaE" xmlns:otp="OTPNA">
<soapenv:Header/>
<soapenv:Body>
  <otp:ProductRequestIn>
     <otp:fromRole>
        <otp:PartnerRoleDescription>
           <otp:ContactInformation>
              <otp:contactName>
                 <otp:FreeFormText lang="NL">?</otp:FreeFormText>
              </otp:contactName>
              <otp:EmailAddress>?</otp:EmailAddress>
              <!--Optional:-->
              <otp:facsimileNumber>
                 <otp:CommunicationsNumber>?</otp:CommunicationsNumber>
              </otp:facsimileNumber>
              <otp:telephoneNumber>
                 <otp:CommunicationsNumber>?</otp:CommunicationsNumber>
              </otp:telephoneNumber>
           </otp:ContactInformation>
           <otp:GlobalPartnerRoleClassificationCode>?  </otp:GlobalPartnerRoleClassificationCode>
           <otp:PartnerDescription>
              <otp:BusinessDescription>
                 <!--Optional:-->
                 <otp:GlobalBusinessIdentifier>-BZNSID-</otp:GlobalBusinessIdentifier>
                 <!--Optional:-->
                 <otp:GlobalSupplyChainCode>?</otp:GlobalSupplyChainCode>
                 <!--Optional:-->
                 <otp:businessName>
                    <otp:FreeFormText lang="?">?</otp:FreeFormText>
                 </otp:businessName>
              </otp:BusinessDescription>
              <otp:GlobalPartnerClassificationCode>?   </otp:GlobalPartnerClassificationCode>
           </otp:PartnerDescription>
        </otp:PartnerRoleDescription>
     </otp:fromRole>
     <otp:Authentication>
        <otp:Username>-USERNAME-</otp:Username>
        <otp:Password>-PASSWORD-</otp:Password>
     </otp:Authentication>
     <otp:productIdentifier type="PDI">---</otp:productIdentifier>
     <otp:lang>NL</otp:lang>
     <otp:ProductInformationType>RIC</otp:ProductInformationType>
     <otp:RequestedPartner>
        <otp:PartnerID>-PARTNERID-</otp:PartnerID>
     </otp:RequestedPartner>
  </otp:ProductRequestIn>

The WSDL file returns 1 function called ProductRequest.

I tried a lot of suggestions and none of them worked so far. I am not sure if I should use the XML in the function ProductRequest with the XML are paramter (didn't work) or i should build up some array and parse that into the argument (didn't work, or didn't do correctly)

The WSDL can be found here: http://ift.tt/16lNAd1