SE only has the email address and that contact form on their site (click on "
Contact Us" link). Just be sure to copy your paypal receipt into the contact box (or forward them the receipt) and let them know your problem. Unfortunately they dont have a phone number for some reason. It's really annoying but on the bright side, they're pretty quick in answering emails.
I emailed them last night and got a response this morning, they said they're going to try to cancel my order but it's not guaranteed. You can try shooting them an email and see if they could cancel it. I suggest emailing them NOW since they're already preparing shipments.