I suggest you unistall the analogue modem, and re-install it.
The Cooexant is an analogue modem, which includes fax (not digital). It uses a COM port ,whereas the USB modem uses a USB port, so I can't see how there can be a port conflict.
When you re-install the analogue modem, they usually set themsrelves up on COM3 (which is in fact a port on the modem board, not a port already in the system.
I would be surprised if there was a conflict, as I've never seen one like that before - but still try the uninstall/re-install first.