Unfortunately, Google Voice no longer works with YouMail.
There is no official confirmation from Google, but voice over IP (VOIP) providers have had their session initiated protocol (SIP) connections cut off, preventing them from working with Google Voice. We recommend switching to YouMail or another service provider entirely. Although you will lose your Google Voice number, you may no longer have access to it in the near future anyways once Google Voice is completely absorbed into Hangouts.
Interested in switching over to YouMail from Google Voice? Just submit a request with “Google Voice” in the subject line.
To learn more about what YouMail has to offer, follow this link.