I'm so sorry about your situation and also guessing that you called them today about your post-interview status? Can't you call them and ask them directly about your status? Like I said before, wonderful program with amazing clinicals, but when it comes to communicating with applicants they're very unorganized. I'm not sure why they don't unify their communication system. Most schools have switched to using login portals for decisions, emails, direct phone calls, and or a combination of all of them. Idk why they tend to do a mix and then penalize the applicants. I was told on interview day to be on top of our post-interview status, yet their emails urge us not to call/email/ bother them, yet situations like this happen. On top of that, if they really cared about their accepted students, they should follow up should they receive no response within 2 weeks because emails can be glitched and letters can be delivered to the wrong places. Updates were lost. Then you have those who handed their alt list response forms on time and randomly be told they've been withdrawn.... and then subsequently accepted after that.
With that said, sorry about my rant, but hopefully this will be of some help. From my memory of the sdn posts in the previous cycle and current cycle about post-interview:
In the 2014-2015 cycle, if you received a letter in the mail, it could either be an acceptance or a rejection. Alt list people got accepted via email and direct phone calls.
For 2015-2016 cycle, not quite sure about rejections via mail or email this year, but you definitely get a letter for acceptance. People who were placed on HFS or alt list received a preliminary acceptance email stating that an official offer of acceptance will be coming in the mail. Enclosed will also be a form to accept or deny your offer. You can either mail the form back or scan and email to the office. There were also some alt list people who were accepted by mail, but never received a preliminary acceptance email. No posts this year about being accepted via phone.
That's I can remember about the ways of getting your decision post-interview. As far as losing your spot if you were accepted, you should be able reason with them. Call them again and ask. Utterly ridiculous to rely 100% in USPS or whatever delivery system they used.