Note... I have a wireless phone system with two handsets. One day I noticed a message waiting light blinking on one handset but not the other. There were no messages from GV, nor no indication. So I thought, maybe my wife recently checked voice mail and the phone hadn't yet cleared itself.
Two days later, still blinking. To fix it, I pulled the battery out of the phone, and power cycled that hand set. Put the battery back in, and it stopped blinking and now has been working normally.
Point is, your phone could have an issue as well if the light is stuck on.