see if you are placing the client section in the correct web.config file. SharePoint has around 6 to 7 config files. http://msdn.microsoft.com/en-us/library/office/ms460914(v=office.14).aspx (http://msdn.microsoft.com/en-us/library/office/ms460914%28v=office.14%29.aspx)
Post this you can simply try
ServiceClient client = new ServiceClient("ServiceSOAP");