Cable doesn't use COM port; it connects to the ethernet or USB port of your computer. I think it's already pretty clear what your options are:
A. Send the fax through the Internet by using a paid service, such as efax, myfax, or net2phone. It doesn't matter how the computer connects to the Internet.
B. Use your Modem as a fax machine and send it through the phone line. This may incur a long distance charge.
depin: please check "modem"'s property from "control panel" to see if a driver was installed correctly; if yes, you need to test the modem by dialing a regular phone number to see what will happen. At last, install a winfax software to test faxing. anyway, this approach is to send fax through phone line.