Some people think I'm a shill for CC, but I have simply been a satisfied customer for years. A lot of other folks here on the forum also have a positive experience with CC. Aside from a sustained network attack that they struggled to overcome, and a brief outage after the hurricane in NYC, they've been rock solid. Their fax mailbox service works every time. And, of course, if you were dissatisfied, you could always port the number out again...no contract.
RE: locally forwarding the number, I don't know what's causing that. Maybe you have got both phone ports enabled to both service providers, by mistake.
Good idea about trying to program it directly into the configuration. See attached. Since GV is not a SIP ITSP, commands in the SIP section are N/A, and I have no idea how the star commands are implemented. Since this is the "Voice Service" section and not the "SIP" section, it's worth experimenting. I haven't tested it, so you can be our guinea pig.