I was issued an F1 visa (valid thru 2019) about a year ago to attend grad school in the US. But I have eventually decided not to attend that program and have come back to my home country in Asia ever since (completed all the steps with the international student office). And I now intend to participate in an academic conference in the US.
I am not sure if I can enter the US with my previous visa or do I need to apply for a B1 instead. And if I do apply for a B1, can I be exempt from the interview and just mail my passport to the consulate (since I live kind of far away even from the closest consulate and I will have to travel to another city and stay there for 3 days just for the interview and I'm trying to avoid all the unnecessary cost of time and money )?