If the note secured by the mortgage was discharged in your bankruptcy (no reaffirmation agreement filed), then all the mortgage company can do is enforce its lien against the property.
They can not come after you for money. By doing so, they are violating the bankruptcy discharge and possibly other laws. You need to either contact your bankruptcy attorney from 2001 or get someone new on the case to consider all the facts (I have made certain normally reasonable assumptions) carefully, including reviewing the current correspondence, the bankruptcy filing, and the court docket sheet. The lawyer will then be in a position, if everything checks out, to enforce the discharge and ask for sanctions including attorneys fees.