Hello and thank you for the opportunity to assist you. My name is ***** ***** I will do my very best to answer your legal questions.
If you were discriminated against because of something such as race, religion, ethnicity, gender, or something else along those lines, then you likely have legal recourse. It is illegal for a business, even the post office, to discriminate against somebody on those grounds. If you have evidence of that type of discrimination, then I strongly suggest that you retain a local attorney to file a lawsuit.
On the other hand, I'm sorry to say that it is not illegal for employees at the post office to be rude and unhelpful. That is a customer service issue and not a legal issue. Accordingly, to win any kind of lawsuit against the post office, you will have to prove that type of discrimination that I mentioned above. It is not enough to simply argue that they mistreated you. You would need to show that if you were a different race, religion, ethnicity, gender, etc., that you would have gotten different treatment.
Does that answer your question? Please let me know if you need clarification, as I am happy to continue helping you until you are satisfied.