Well if certified transcripts did not help I believe you've done all you can. Find out if the degree you have matches what they're looking for in the employment. You have not court relief option so just keep looking.
Your potential employer is not required to hire you in this at will employment state. Unless you can convince them to look further into your education and accept your foreign qualifications, you are probably out of luck. Sorry.
My instincts are telling me that the potential employer is not being fully straight-forward with you.
The evolution of the name, ownership, location, organizational status, and other facts about a post secondary school, college or university is relatively easily traced and documented. If you have truly made the factual showings that you described here, then the prospective employer has more than sufficient data to know that you have not been dishonest in your representations of your educational credentials.
More likely, during the period that the issue was unresolved, the employer moved forward toward another candidate, or found another reason not to persist in the decision to hire you.
Now, there is institutional or individual discomfort with disclosing the true circumstances of the issue to you.
This is unfair and hurtful, of course. Perhaps you can look at it from another point of view: if this is a preview of this organization's practices, maybe this would not have been such a great employer?
In all events, you have not stated any sound factual basis for a legal claim here. Under at will employment law the employer does not have to state a reason for not hiring you and does not have to be truthful in any statement of its reason. Reneging on the offer is also not unlawful.
I am sorry that you have had such a demoralizing experience.
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