Google Voice is a total mess, and as a “free” consumer service that Google has shown little interest in maintaining and supporting, you don’t get any kind of support or help whatsoever.
My sincere advice (if you’re a free Voice user) would be to delink your Google Voice number from all critical services. Get a real phone number for which you have the ability to get customer support.
Google Voice is probably my favorite Google service... I have looked at alternatives many times in the past and have never found anything that compares that isn't super expensive (and usually not as good). I really hope Google keeps it. But I am prepared to migrate if Google shuts it down (and I really hope they provide a seamless number porting experience if they ever do...).
Their own internal teams as well as game studios didn't know about Stadia's end until the day it happened, what makes you think they'll treat you better with an unpaid service?
You can trust google they will let you use forever and won't block your account anytime without warning though.
(Perhaps this is just dread since I use it for the same purpose)