Bankruptcy Law Questions? Ask a Bankruptcy Lawyer.
If your bankruptcy (I'm assuming a Ch.7) was actually discharged, you cannot "cancel" anything anyway. If you do not make the payment to the trustee, however, you could be in trouble with the bankruptcy court and they could take action against you. If the trustee chooses to collect on that money, your credit could suffer. You'd be wise to pay the money and go on with your "new credit" life.