Their message actually says the number is "unallocted" (unassigned) when you try to call them back. For these clowns just another way of them using a phone number and their no-answer message saying the phone number has not yet been assigned to a client/customer.
For Us (the consumers) - just another way that we can determine they are fraudulent/scammers, as any legit company would identify themselves correctly, by company name, when we attempt to call them back.