Your setup is just like ours. We have had problems before but we thought it was with using VPN. Weird. I thought at one time it was the credit card.
We have never really nailed it down.
That’s what I thought when it happened again today - maybe I entered the card number incorrectly; but I was told precisely that it was due to the phone number. (Maybe they don’t have ways to ‘verify’ a VOIP?)
I called up and worked it out with them, but we shouldn’t have to go through all of this.