Conexant HDA D330 MDC V.92 doesn't connect in Asia

I recently replaced my Inspirion B130 with a Latitude D630.  Modem in Inspiron was the Conexant D110, modem in new Latitude is Conexant D330.  everything else - software, ISP, etc all the same - but Latitude's modem doesn't connect to my ISP here in Sri Lanka (Asia), thought the Inspiron does.  Have tried everything I can think of to no avail.  It dials fine, but most of the time does endless handshaking without connecting.  When it does connect, it's not useable - i.e. if I click on explorer or Outlook or whatever, it says" not connected to internet" or "server not found"  and usually disconnected within a few minutes.  Driving me mad!  Must have dial-up access; am humanitarian worker in conflict zone - really need access 24/7.  Any help most gratefully received.