Hi and a warm welcome to FlyerTalk.
Delta ceased to be a partner of VS earlier this year so you will not be able to redeem your flights with them. It's strange you weren't informed of that when you called.
Can't answer your question regarding VX but you can always redeem your miles with VS' other airline partners. I wouldn't waste them on internal US flights, I think they represent poor value for your mileage. VS offers excellent award rates from the US West Coast to Japan and Hong Kong for example. A First Class class award round-trip ticket from SFO-HKG with Singapore Airlines can be yours for 130,000 miles. Or fly LAX-NRT round-trip in F for the same miles. If you have no intention of redeeming your miles for VS flights then SQ offers some of the best deals on F awards from the US to Asia.