So in your view, being hired by the temp agency was a mere formality.
Employment at will is the default rule where an employee does not have a contract. Under that rule, either the employer or employee can terminate the employment relationship at any time with or without good cause and without notice.
Unfortunately, it appears the employer exercised its right to terminate your employment without good cause or notice, which is a harsh result, especially if you feel the employer misled you.
If the employer made promises they never intended to keep, and you can prove that occurred, and you reasonably relied on those promises and suffered damages as a result of your reliance, then you could potentially sue the employer for fraud.
Otherwise, there would normally not be any legal resource against an employer in this situation.
I hope you found my answer helpful, even if the law is not in your favor. I would be happy to clarify my answer if anything is not clear or you are looking for additional information. All the best to you!