I very much doubt that you will be able to clear this problem at all. It will need a system administrator at Yahoo to do it.

Despite the many posts on this forum to the contrary, I have found that emails to Yahoo Customer Service do get answered the next day, provided that the problem is clearly explained to them. Your problem should be easy enough for a Sys Admin to fix, so give them a try. Tell them exactly which chat room you were in and the date and time you got stuck there (so they can find you quickly on the log) and ask them to clear the flag which is holding you.

But if nothing happens, you will probably have to walk away from your past and create another account for yourself.