Your story sounds exactly like ours!....on the west side of the country! My spouse uses the oxygen only at higher elevations. But we also travel with the concentrator and bottles, using and needing exchanges just like you. And just like you, have had the same runaround! Same thing about faxing the Rx. We carry a copy of the Rx with us in case that helps us (which it may or may not). The whole thing is so frustrating that we've considered buying a portable oxygen concentrator ourselves, to use instead of bottles, but they are quite expensive. Have you looked into them? Something like the Inogen G3.
So by any chance does your nationwide provider start with an "A"? I don't know if it's appropriate to name companies on this forum, just as part of discussion like this.
We've also had bad and frustrating experiences with this company at home. In our area, they just never seem to have their act together. My spouse is on Medicare, and unfortunately, has to wait 5 years (from the beginning) to change companies. It all has to do with the payment situation. Perhaps if you are on Medicare you know about this. Anyway, we will look into changing providers once the 5 years is up.
I wish I knew of a good solution. But if you ever find one, please post or PM me. We only know of one other nationwide provider, name starts with an "L". (Again, can we name the companies here on the forum?)