A discharge is not the same as having the case "closed." If you have a Chapter 7 "asset": case, then the trustee may still be administrating the assets for the creditors, and during that time, which can take months (or, even years), the trustee can continue to request information from the debtor as necessary to administrate the assets.
If you have a "no asset" Chapter 7, then there is nothing to administrate, and the case should generally close almost immediately after the discharge.
Once the case is closed, the trustee has no more authoirty and can't request anything from the debtor. Prior to closing, the debtor must continue to cooperate with the trustee so as to permit the reasonable administration of the bankruptcy estate. Bankr. C. §521(a)(3).
Hope this helps.
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