I have an AT&T phone Dect 6.0 and when the phone rings 6 times and then a "fax" sound comes on. I do not have a fax hooked up. It reads "no line" after the phone stops ringing. How do I fix this? There is no model number on the phone. The numbers on the phone are IC1135B80730100, and FCCID EW780-730-00. That is all I can find. I have not been receiving messages for 1 1/2 weeks. I didn't know that my machine was not working. I did not do anything to it to change the setting. Please advise.