Redirection to non-existent voicemail

Once in a while my cordless phone's voicemail light starts flashing, the display shows a message is present in the answering machine, but there is no message.  When I call my home number, I'm redirected to some voice mail system I know nothing about - the cordless phone rings but the answering machine never picks up.  When I dial *99 I am asked to set up voicemail (which I don't want to do) and this clears the flashing light on the cordless phone.

This is an intermittent problem and is extremely annoying since I may be losing calls.  What is going on here???  A few of my relatives (also using Comcast) have the same problem.