Well there are probably many answers to this question, but let us go to the two big ones.
First answer — that debt was not discharged, or in other words, not “in” the bankruptcy. Debt that was not included in your bankruptcy includes:
(1) Student loans
(2) Many tax debts
(3) Debt arising from fraud or similar
(4) Debt arising AFTER YOU FILED the bankruptcy.
Second answer — if the debt being collected after discharge WAS included in the bankruptcy and was discharged – -just an ordinary credit card or personal loan, for example, then the debt collector is breaking the law.
WHAT do you do to stop a collector who is unafraid to break the law?
(1) Send them a copy of your bankruptcy discharge notice — whatever paperwork you got saying you had a discharge, send to the creditor — certified mail — and explain this debt was covered. Tell them on the phone as well – -giving your bankruptcy case number may be enough.
(2) If (1) does not work, call a consumer attorney (find one at http://www.naca.net – -which is NOT the mortgage help website, it is for legitimate consumer attorneys of all types) or call a bankruptcy attorney, including your former one.
You submitted yourself to the bankruptcy system, with all its punishments and benefits, and the main benefit is your fresh start. If collectors are calling and your polite notice “Hey, I filed bankruptcy and here is the proof” does not stop them from trying to get you to pay this discharged debt, you can enforce your rights in either bankruptcy or state or federal court — hire an attorney and tell those bullies to leave you alone!!