changing fields - Terms agreed upon for PhD offer are being unilaterally rescinded—what to do?

At my old university:

I was a visiting researcher at a university, working with my current advisor. My advisor got an offer to go to another university. He also offered me to join him at his new university.

I got an offer letter by the Admissions department of the new university for their PhD track. As the offer was lacking in multiple regards -- type of housing, healthcare, stipend rate, academic responsibilities, opportunities for internships -- I spoke to my advisor, Admissions and the dean of my department at the new university.

My advisor and the dean effectively agreed to fixing my concerns. These agreements were partly put on record. During that time, my advisor had not yet accepted his new position. (Maybe the dean just agreed to my concerns in order to land that hire.) I was invited for a short stay as a visiting researcher.

At my new university:

During that stay many of my concerns materialized. I voiced my concerns with my advisor, the respective administrative departments, and Admissions. My advisor reluctantly tried to change things, but mostly referred me to speak with other people.

This effectively led to a one-sided invalidation of my offer letter.

I spoke multiple times with my advisor and the dean. They still are of the opinion that they are bound by our agreement. However, they are now telling me that they are in no role to give orders to the Admissions department. The only two people who have this authority is one of the Vice Presidents and the President himself. The dean knows that this Vice President will side with Admissions. The President is shortly before his retirement and will not be present anymore.

Both my advisor and the dean made the impression that they can take care of my admission and fix my concerns. Now they are saying that even though these things were agree upon, they cannot do anything to fulfill their promises.

Current options:

My advisor offered me to work from another country as a remote contract worker with lower effective pay. That will of course not lead to earning a PhD.

Legal options are not available, as the university is located in a country with no court system.

How would one go forward with this situation?