OK, so the GV number still works. That's great. But, you've misunderstood how Google Voice works: it is a service, just like Gmail, Calendar, Contacts, Docs, Maps, etc. All Google services are tied to a Google account (a Gmail address). You might have signed into the OBiTALK web portal using some other/old Gmail address, but the actual Google Voice configuration is independent of the address you used to sign into your OBiTALK portal.
If your Google Voice phone number was transferred from
abc@gmail.com to
xyz@gmail.com, you need to replace your Google credentials on the OBiTALK portal.
So, at a minimum, sign into the portal. Click on your OBi 200. Click on the trash can icon to the right of the SPx that you had set up with Google Voice. Wait for the device to be remotely rebooted.
Meanwhile, open a new tab in the same web browser (Ctrl-T). Sign into the correct Gmail account that now holds the GV number. It can be different than the one you used to sign into the portal.
After the device is back online, click on the SPx again, and follow the instructions to set up Google Voice. When you get to the step where it pops up a window to show you your signed-in Gmail IDs, pick the correct one that holds your GV number, and complete the process. It should now be able to make and receive calls.
If this doesn't work, then you need to factory-restore the device and start over from scratch. It only takes about 10 minutes. See my instructions here, starting with the bullet list:
https://www.obitalk.com/forum/index.php?topic=13868.msg89076#msg89076