The last time you brought this up, you correctly surmised this is a complex legal issue that you should probably get legal advice for and not rely on the message board.
However the legal theory you are probably searching for is called an “implied contract.” Sometimes, certain behaviors, in certain contexts, can create an implied contract, which could be enforced by a court later. The wrinkles, caveats, local statutes, and complexities around that are simply too vast to delve into for your personal situation IMO, you need a local attorney. Which I believe you understood the last time you posted about this.