Then I would call them and say I need to rethink the numbers to stop them from going forward.
Also, I would seek a different VA lender. I think it is pure BS that they cannot give you even an idea. I would tell then to hold the underwriting then also seek a new lender.
I have a score of 655 and went to a VA lender. After pulling my credit report, they could tell me right away how much they can approve me for. I didn't even tell them how much I wanted. I say try a different lender. Also ask the lender how much their origination fee is. It should be no more than 1%. Even with 1% try to talk them down.