In most cases, if your bk was a no-asset Ch 7, then ALL pre-petition debts are considered discharged whether they were listed or not. That should be your position too. If the collections get aggressive, you can always re-open your case to add the debt.
On discharged debts, ANY collection activity, including placement of a collection on your reports, is a violation of your discharge and you could nail them with contempt charges for it. Write them a letter and tell them if they don't stop their illegal actions, you will pursue contempt charges against them in bk court.

