When you received your email, did it state that you were banned, or that your account was suspended due to an investigation? (then followed by an email banning you?)
maybe better for you ... if they don't pay these webmasters who've been sending them traffic for months and who've now been banned without warning, you may literally be better off without them
It's possible I'm not supposed to do this, but oh well. Verbatim: We have terminated your Yahoo! Publisher Network beta account [ACCOUNT ID] for breach of the Terms and Conditions and/or Program Policies. Your breach includes but may not be limited to sending traffic from users located outside the United States, in violation of Section 11(l) of the Terms and Conditions. In accord with Section 6(a), we will not include such amounts in your payment. We have refunded amounts generated from the non-US users to our advertisers and will pay any remaining amount owed to you in accord with the Terms and Conditions.