Hey,
I have wrote several web services myself for a "Big Bank" and the best tool to use is soapUI
http://www.soapui.org/. Very easy to use.
The WSDL is not published
What do you mean by the WSDL is not published? It should always be... That's one of the fundamental piece of SOAP. Do you mean there is no "publicity" about them or they aren't available at all? If they aren't available, then soapUI isn't the best tool...