I would suggest something like:
Hi, My name is XXX. I applied to XXX and hadn't heard back from you. I wanted to confirm that you had received all of my materials and to see if there were any other materials you needed.?
A: no we have everything
Ok. Thanks. By the way, any idea what your interview dates are going to be? I want to make sure to leave a space for your program in my schedule if you do invite me!
Answer 1: Oh, we already gave out all our interviews
or
Answer 2: Those dates will be on XXX and XXX
If answer 1:
Thank you. (problem solved, you weren't invited)
If answer 2:
Any idea when we'll be hearing?