Google Voice Voicemail Stopped Working

I've been using Google Voice to handle my voicemail on my cell phone for a long time.  In the past few months, it stopped working.  I have no idea how or why.

I just fixed the problem.  I did this by logging in to Google Voice, going to Settings, and going to the Phones tab.  From there, there were four steps:

• I deactivated voicemail on my cell, then 
• I deleted the cell number from my account, then 
• I added the cell number back to my account,
• The new Google Voice UI doesn't work, so I switched to the Legacy Google Voice UI, then finally, 
• I activated voicemail on the cell.  This had me dial *71 + the my Google Voice number.  I'm not sure if the other steps are necessary or if I can just dial this in the future.

I don't know whether it would have been enough to deactivate, then activate voicemail.  I didn't try this.

Edit - June 16, 2017: Google has updated their interface for Google Voice.  Unfortunately, I couldn't figure out how to set up voicemail in the new UI, so I had to go back to the Legacy Google Voice.  I added that step as the fourth step in the process above.