I want to disable google voicemail as well. It picks up after 2 rings!!
These are googles directions..
On your computer, open Google Voice.
At the top left, open Menu Menu and then Legacy Google Voice. Google Voice will look different, but you're in the right place.
At the top right, open Settings Settings and then Settings.
Click the "Phones" tab.
Under your forwarding phone, click Deactivate Google voicemail on this phone.
Follow the instructions to turn off Google voicemail.
But THERE IS NO forwarding phone or Deactivate Google voicemail. Those options are NOT there.