Is it legal for my mortgage company to send me demand letters after I surrender the property in bankruptcy?

No. Unless you had signed a reaffirmation agreement, when you surrender a property in bankruptcy your "personal liability" is discharged or cancelled by the court.

If your mortgage company continues to try to collect the debt (as opposed to foreclosing), they are likely violating the bankruptcy court's discharge order. You may have a lawsuit or claim against your mortgage company if they make efforts to collect a discharged debt.

It IS legal for them to foreclose on the property after a bankruptcy, and they are required by law to send you certain letters to accomplish that. But they are not allowed to seek collection of the debt as your personal liability after the debt has been discharged in bankruptcy.

J Thomas Black
Board Certified, Consumer Bankruptcy Law- Texas Board of Legal Specialization