My account was recently banned because I used a transfer cable to switch consoles (old to slim) and it was market place thieft somehow... but anyways...
Step 1: Call Xbox Live Support and go to cancel membership/credit card information
GIVE THEM YOUR REAL INFORMATION ON THE BANNED ACCOUNT
Step 2: Go through the steps to show that your the account owner, then ask if they can remove your credit card so you aren't charged without being able to play.
Step 3: Just go on and tell them you were banned and you still had some gold left on your account and ask if you can be given Xbox Live Gold Tokens equal to the ammount of remaining time you had. They'll tell you to wait and give them your email address. GIVE THEM A REAL ONE
Step 4: They'll email you the tokens and say okay thanks then ask them if they'll stay on the phone with you while you check to see if you got it. Then check your email and tell them that you did not get it & they'll send you another set of new tokens without cancelling the others! Tell them that it didn't work and to try a different email address. They'll send a 3rd set of new tokens so you'll have 3 times as much Xbox Live time as before!
Step 5: Make an offline account, name it anything you want. Then follow this tutorial to copy your banned accounts gamerscore: http://www.xboxmb.com/forum/16-xbox-...e-another.html (I dont take credit for this link)
Now you have 3 times as much xbox live time and all your achievements back as well as a new gamertag.
I had to go through this myself and thought it would help you guys :)
All of this (except the copy gamer score) was found by me!
Hope this helps anyone who got hit by the ban wave!
Btw I am ThE KiiNG JAMEZ from Se7ensins.com and Bawlz from XboxMB.com
I just thought I should post it here too