I have an analog set that cannot get incoming calls. From the outside, it says its a non working number, although it is a DID. And when dialed internally, it just gives dialtone. It CAN make outgoing calls! I changed the TN and I tried another analog set.....? Could this be just a bad feed pair? If so, I would think it wouldn't be able to make outgoing calls either if that was the issue? Please advise, thank you.