HAD THIS PHONE ABOUT 2-3 YEARS N0 PROBLEMS, BUT SUDDENLY ALTHOUGH A CALLER SEEMS TO BE LEAVING A MESSAGE FROM THEIR END - THE GREETING PLAYS ETC, NO MESSAGE IS ACTUALLY RECORDED. WHILE THEY ARE TRYING TO LEAVE A MESSAGE THE 0 FLASHES ON THE DISPLAY ON THE BASE SET BUT THERE IS NO MESSAGE. THE MEMORY IS NOT FULL, AND IT IS NOT SET TO GREETING ONLY. ANY SUGGESTIONS PLEASE