We recently cancelled 2 of our 4 phone lines, and they happened to be CO 2 and CO 3 on our Panasonic PBX TD816. How do I let my PBX know that those 2 lines are no longer active CO lines? Otherwise when we want to make an outgoing call and the CO 1 is in use, dialing "9" will go to CO 2. Also, if CO 1 is in use, incoming calls will hear a busy tone. Thank you.