The service is expecting Soap 1.1 (Content Type: text\xml), where the WsHttp binding uses Soap 1.2 (Content Type application/soap+xml)
You may like to use the customBinding, instead of WsHttp
On Binding Tab, Binding Type = customBinding, textMessageEncoding -> messageVersion = Soap11
A big gotcha will be the message level security, you will need to right click CustomBindingElement -> Add extension -> security. This is where it gets tricky. You are dealing directly with the security extension ( the WsHttp binding hides most of this).
Might be easier if you ask the service provider to support Soap1.2