I tried changing the ooma settings to wait 7 rings before voicemail hoping GV voicemail will pick up first, but it still goes after 5 rings and goes only to ooma.
All the call records still show up in GV but I can't get it to consistently and exclusively go to GV voicemail.
See if your settings are as below:
Auto Answer delay: GVE will wait this amount of time before automatically answering a call to play the call presentation announcement. If you are not using call screening with Google Voice, you should disable this.
Auto Connect delay: GVE will wait this amount of time before signaling Google Voice that you picked up the phone to answer/intercept a call.
ListenIn Delay: GVE will wait this amount of time before signaling Google Voice that a call should be transferred to voicemail for ListenIn. Changing the Auto answer delay will change the timing of ListenIn. If the ListenIn delay is not set correctly, the call may hang-up before the ListenIn feature is triggered.
12 seconds (default)