Just confirmed with Disney that we are able to do the B2B because we are not American
I would question that. The law says "no foreign-flagged ship may carry passengers from one US port to a different US port without a stop in a distant foreign port". No mention of "only applies to US citizens".
While your 2 separate cruises, individually, are legal under the Passenger Vessel Services Act (cruises to/from Puerto Rico have a waiver), since you are doing back to back cruises, the PVSA sees
your cruise as from New York to Miami, and is illegal under the law.
Did you just ask the person answering the phone? Or did you ask to speak to a supervisor (or someone higher up)?
Did you actually say "Why doesn't the PVSA apply?"
Disney is fairly new into this PVSA world (check out what happened with the first Alaska cruises from Seattle a few years ago). Even cruise lines that have done it for years also will mistakenly book people on cruises that violate the law. And the immigration people won't catch up to it (when they do) until much closer to the cruise causing cancellation penalties, air flight changes, a real mess for the passenger.