Thank you for trusting your question to JA today. I am a licensed attorney with over a decade of law practice and over 20 years of experience in the legal field. I’m happy to be of assistance.
A common misconception about HR is that they are neutral or supposed to be neutral (some even think there are laws requiring this), but it's entirely untrue. HR works for the company. They help employees to the extent that it helps the company and that is always their goal, so it is not shocking to me that HR seemed hostile towards you.
In employment law, hostile work environment does not mean what many people think it means. It does not mean a place of work that is generally hostile or contentious. Instead, according to the Supreme Court of the U.S., it refers to a harassing workplace where the harassment itself is based on race, religion, gender, age, disability or FMLA use. You didn't mention any of these things in your question, so I am concerned that you aren't alleging any of those things. If you are not, then legally the employer doesn't have an obligation to address the complaint and HR can instead work towards terminating you, if that is the company goal. This is because, in employment law, if you don't have an employment contract that expressly states you can only be terminated for cause, you can legally be terminated at any time. This is called "at will" employment and makes up nearly all of us, as employees.
Unfortunately, if you have no contract and you are not alleging discrimination based on one of the factors I mentioned, you rights are restricted to whatever they have as an internal company policy (which I can't address).
Now, if you were alleging (or are now alleging), discrimination based on one of those factors, and HR is not helping, now is the time to contact the EEOC in your state (unless FMLA and then you contact the Department of Labor) to file a complaint.
If you have any further questions, please let me know. I invite follow up questions, so use REPLY for those. If you have no further questions then good luck going forward and please do not forget to rate my service with a top-three rating so that I receive credit for working with you today. Also, feel free to request me in the future, if you have questions concerning a different matter.