Hanging up the modem

I have a particular problem with my computer. I have dial-up(not the
problem I'm speaking of) and my modem likes attain a state where the modem
is still off-hook, but isn't allowing socket connections.

What I need is a sledgehammer "ATH0" to what seems to be com3, but
everything I've tried so far detects the modem being off-hook and won't open
the port so I can hang it up.

Suggestions?

David