Can 2nd Mortgage collect after sherrifs sale (live in Mi)?

House forclosed, sold in sherrifs sale in Jan 06 never heard anything until 2 weeks ago from debt collector stating we owe what it didn't sell for. I have been hearing from sherrifs dept and realitor that they cannot collect if no bid was made, but they are not lawyers and really couldnt give answer, if anyone has any information please let me know.