Did you try connecting with a modem, does the system trip ringing? IIRC the system only responds when it hears tone from the incoming modem connection. If the modem isn't responding, you will need to check the dip switches on the CPU as the modem connection can be redirected to the second connector on the CPU.
Don't delete the lines, just make them busy using CMD E51 and just to make sure change them into a different trunk route in CMD 3000.
Is reception a console or just a Dterm?