I would try to connect to your Sharepoint site with this tool here. If that works you can be sure that the problem is in your code / configuration. That maybe does not solve your problem immediately but it rules out that there is something wrong with the server. Assuming that it does not work I would investigate the following:
I think there is nothing wrong with using security mode Transport, but I am not so sure about the proxyCredentialType="Ntlm"
, maybe this should be set to None.