If I was promised a job but then denied, what should I do?

The law does not enforce "gratuitous promises," or promises you gave or did nothing in exchange for. Therefore, if you were promised a job but did not have to do anything to get the job, or did not change your situation to your detriment in some significant way in reliance on the promise, it is not enforceable. The times a promise is enforceable are:

1) If there is an actual contract. To be contract, there must be an offer (e.g. of a job), acceptance of the offer (e.g. you take the job), and an exchange of  consideration, or things of value--for example, to take the job, you had to undergo some training or get some certification, which you did.

2) If the prospective employer promised you a job, knowing that you would have to do something major, like relocate or give  up an existing job, to take the offer; it was reasonable for  you to believe and rely on the job offer; and you did in fact rely on the offer and do that major thing to your detriment, like relocating or leaving a job--if all those criteria are met (including that the employer knew  you would do something to your detriment in reliance  on the offer), then you may be able to enforce the promise under  the theory of "promissory estoppel."

But again, if you were promised a job but did nothing to get that offer or in reliance on that offer, the promise  is unenforceable and the prospective employer may disclaim or renege on it at will.