My withdrawals from schools:
School 1: I forgot to check off the "I will not be attending" box and mail it back to them. For some reason, I ended up putting the letter away and assuming no response = not attending. They called me 2 weeks after my "deadline" for the deposit, and asked me what was going on. I was told to send them a withdrawal by email so they have it in writing. I wrote something like:
"Dear [person who called me]:
I am kfire326. I spoke to you on the phone earlier today. I will not be placing a deposit for XYZ medical school. [apology for my mistake, i appreciate consideration/acceptance, blah blah blah]
Thank you"
School 2: I got the acceptance with a piece of paper saying something along the lines of, "We're sorry for the inconvenience, we'll have the acceptance packets out in the second week of February," so all I got was the letter itself. I got a 3 week extension in writing from the dean of admissions himself, and he apologized etc etc. He promised that the acceptance packets would be delivered by then. That new deadline came and went, and still no acceptance packet...I haven't contacted them, and I don't plan on it.
School 3: These people were complete a**holes to me whenever I called. Friends of mine say the same thing. After an Interview offer, I emailed the admissions email address and just said "Dear ____ admissions: I was recently offered an invitation to interview. I will not be coming in for an interview, and would like my application for your M.D. program withdrawn. Thank you." I didn't really care to be professional with them, since they were not professional with me.