Look through your logs, profiles, hb settings etc. Try to work out what caused you to get banned.
examples:
botted 24/7 over the weekend
got stuck in the middle of a city for 10 hours
whispers you may have received
someone reported me - see above
stuck battle ground bot
etc...
work out what you think the cause was, and play it to your advantage.
caught botting 24/7 = just busted up with my girlfriend, so I burried my head in wow
caught flooding the ah = broke my leg so I cannot go out, so I thought I'd empty/sell items in the guild bank
caught stuck in the middle of town = your screwed! (but there is always the "my brother has a mental illness, he was playing at the time) Yea I know... harsh, but it can work (sorry to anyone who has been touched by mental health issues, me and my family have)
Phone 'em up, email is slow and not too effective imo. Sound shy and slightly hurt that you cannot play any more. Never shout or swear, cos the people you talk to are not likely to be the people that banned you. Win their sympathy, don't spill too much too quick. And most of all ACT DUMB, even if you're a quantum physicist, pretend to know nothing about computers and tech. What you want them to think is your a bit of a no lifer with nothing better to do than play wow for hours on end.
Be creative, if you've not taken precautions, the "I got hacked" isn't to effective when they have "cold hard data" to prove you're not telling the truth.
Good luck