When I say "please use my contact form," what I mean is "please use my contact form." Not "please dig up a personal email that you have for me from some point in the past." Not "please use the contact form at miragrant.com." If I meant either of those things, I would say so. They would look like "you can only win if you already know how to reach me ha ha" and "please use the contact form at miragrant.com," respectively. If you do not use my contact form, at the seananmcguire.com website, you will not be eligible to receive your prize.
Sometimes the rules by which I live my life may seem fiddly or arbitrary, but there are always reasons. Please, if you want to receive something free from me, follow the rules which I have set for that reward.