The bank don't know what they're talking about. The car won't have a registration number until its registered (obv) which will be your personal number. It will have no other "proper" registration number (I assume they're referring to a year specific one).
As to the VIN, the dealer will have it or be able to get it from the factory.
As to why the bank wants this info, I have no idea as I've never been asked it.