There are a lot of phone verification services in the market today & I’m guessing your number is being flagged when you call these companies because of your service provider, not VoIP. I can check next week, but their are services you can register your number. Even though I work for a billion dollar company with 2,000 employees, we’ve had to register our two main main customer service numbers because they were getting blocked by the cell companies.
I’m surprised that these companies wouldn’t have different process for companies that they don’t trust like not shipping until funds clear.
I doubt it’s my internet provider. And again, it’s only failed to work with a couple of companies; but they’re big ones, not obscure ones.