I received a new NBN black box 20/8/20. Internet has always worked fine. Since getting the new box, phone calls sporadically don't work and I get a voice message "The number you have dialled is not valid". Usually the VOIP light is flashing when this happens. If it's solid green the phone works fine. I've read the other posts with the same problem that recommend re-starting the modem. I'd prefer to find out what the problem is. Is TPG able to test my line their end? I've had my account with TPG since 2015 without incident so something is not right. This is a real problem as I'm getting an important call on Wednesday and want this problem fixed by then.