How to run my Play Games with its correct game progress after it runs another Play Games account of the same game app?

I have this problem as a game user. I have contacted the game developer and they told me that’s an issue of google instead of their game.

I have an old phone A with a Play Games account A that saved my game progress A. I have another old phone B with a Play Games account B that saved progress B.

I now have a new phone C that signed in both Google accounts A and B. When I opened the game, it loaded my game progress A, but actually, I wanted to load progress B.

Therefore I signed out my Play Games account A in the game settings inside my game, and signed in my account B. Restarted the game, but it still didn’t load progress B.

So I cleared the cache and data for both Play Games, Play Store, and my game app. I uninstalled my game app. Then I switched to my account B in Play Games and installed the game app again. However, it still only ran progress A.

So I gave up to play progress B in my new phone C, and opened my game in my old phone B. Turns out my old phone B, even it only logins to Google Play account B, runs the game with progress A. None of my phone seems able to load progress B anymore now.

Does that mean my Google account A overwrite game progress A onto B? How is this even possible and how can I fix it? Ideally, I want to run progress B in my new phone C. Or, at least my old phone B runs my game progress B back again.