That just completely sucks. I feel sorry for you man.
I couldn't actually find a contact section in Yahoo for you.
However, I did find this:
Yahoo wrote:Custom Leagues
The commissioner has the authority to lock any team at any time without warning or explanation. If your team has been locked, you may attempt to contact the commissioner via the league message board (if posting privileges remain) or through the email address displayed on the Team and Manager List page.
The commissioner is not obligated to respond or to justify his/her actions. Yahoo! Sports does not interfere with Custom League matters. Yahoo! Sports will not restore access to teams that have been locked or contact league commissioners on behalf of locked members.
Because the commissioner has full authority over Custom Leagues, we recommend choosing your Custom Leagues carefully.
Source: http://help.yahoo.com/l/us/yahoo/baseba ... ll-73.html
Therefore, contacting them might not help I'm sorry.