I have two telephone numbers: one for my private calls and one for my business calls and fax. I have one line coming into the house with the typical red, green, black & yellow wires. The cable company said that a single jack with a dual telephone line would work perfectly. Unfortunately, the fax does not pick up the incoming fax. I am trying to put a dual modular jack in to have separation of the lines. I have the top jack connected red to red and green to green; the bottom jack yellow to yellow, black to black. I have only the top jack getting a dial tone. What am I doing wrong?