I did a quick Google search on the topic. It seems like Amazon regularly shuts down accounts with too many returns, Abuse of Policy. Sounds like that's the issue here. Whether it was you or as said in their email, one connected to you, they still shut you down because:
"We've found your account is directly related to another account which has been previously closed for abuse of our policies. As such, your Amazon.com account has been closed and any open orders have been canceled."
Sounds like you're out of luck here. I also don't think there's anything anyone here can do for you. You have to deal with Amazon if you want the account re-instated. Sorry.