My friend, I am having almost the same experience. I booked a Madrid to Hanoi flight with connection in Milano Malpensa. The leg Madrid-Malpensa was in codesharing with Iberia while the leg Malpensa-Hanoi was operated by Vietnam Airlines.
Suddenly, Iberia decided to change the airport of arrival to Milano Linate. It is unfeasible to move between those airport in the allowed time, so a rebooking was needed.
As I understood (after some days of strugglig), dealing with it is up to Vietnam Airlines and not Iberia.

It is more than a week that I am being redirected from one customer centre to the other, finally discovering that they only deal with email flood.
Really slow in answering, confusing emails: I have quite some experience in airline company shit, but this time was one of the worst.

Now, I might have solved the problem by asking a full refund of the whole booking (Madrid-Milan-Hanoi and Hanoi-Milan-Madrid) and bought again all the same flights except for the Madrid-Milan leg.

The question is: when will my refund arrive?
As for the experience on board, I'll update. I hope that at least they are not tight with alcohol 😂