Hey Michael, I'm sorry to hear that you account has been compromised. There are a few solutions to this issue.

First, if you are in any private/custom leagues, you can contact your league commissioner. There is a 'Transfer Teams' tool that the commissioner can use to transfer your team to the new ID.

If you are in a public league, you will need to contact Yahoo! by email to verify ownership of your team, and troubleshoot this issue further. I hope this helps!