i totally remember when you were going through this originally.
It's awful that you are going through this and that the HR person isn't even giving you the respect of a phone call to tell you what is going on.

Here are my suggestions as an HR professional:
1) Talk to your manager and ask them directly about the situation -
Make sure you mention that you are happy to stay in this position but tell them you never heard back about your original interview and that you'd be very interested to know why you didn't get the job...for future personal and professional development.

2)I don't know what kind of company you work for, but if the HR person is in your building, is it possible for you to stop by, since they aren't answering your calls, and just ask in person what's going on...if you have the confidence to do this. You may have to handle a rejection.

3) Your other choice is to suck it up for now and not do anything, and decide if you are comfortable staying where you are, or maybe changing companies at some point.

Personally, I'd want to know something about what happened, and I've been lucky enough to work with people and for companies that provide feedback on things. I am also very obsessive and it would really make me stressed to think about...so you have to decide which is worse...obsessing for however long about "what happened" or finding out what happened and getting information that may be upsetting. i've gotten some interesting feedback on interviewing and even my personal style...and I interview people for a living...but have learned not to take it personally and have been able to overcome those constructive criticisms.

Feel free to PM me if you want more advice.

Good luck with whatever decision you make!