You can either call and speak to your lender or the agent that is conducting the Trustee Sale. Who issued you notice of Trustee Sale? Have you looked it up on their site or called them?
A couple of typical paths we take to find out. I would start with the Trustee site and then call them, doubt they will try and collect or chase you down just because you request clarification on the date
firstname.lastname@example.org if you would like to communicate privately.