Re: the google telephone number does problem with phone number
As an interim solution I think you have two options:
1. Remove the forwarding number and have it show your normal number (I know you will lose tracking data, but at least the phone will ring).
2. Delete the extension and try creating a new one from fresh. Although you may not want to risk trying this in case the same error occurs and you end up with no phone enquiries.
After taking one of the above actions I'd recommend you contact Google Support and figure out if this is a bug, or if there's anything wrong with settings.