need to get visa stamp from old passport to new passport

G'day,
I've enquired about the same thing.  The Aussie consulate told me they could organise an "exit visa" letter.   

You take that letter to the Vietnam immigration people and they organise it "apparently" , and put the visa transfer in your new passport.     Maybe the should have advised you of that when they handed you a blank passport . 

They probably assumed you would apply for an extension if that's possible given all the issues with that.

I would contact your US embassy for advice on exiting the country.   Surely they must have known there was no visa in the new passport &other old one is now cancelled.

Wasnt there enough room in your old passport to get the exit stamp from Viet Nam. The embassies dont inform the VN government when you get a new passport, so you could have still exited on your old passport, but not now with two holes in it.

I think you have to get a new visa.  My passport was expiring and had to get a new one.  I was told at the time (about 5 years ago) that a visa is only valid for the passport it was issued to and cannot be transferred.  So after getting my new passport , I submitted my old and new passport to immigration and got a new visa.  Hope this helps.