Your lawyer said it right that you cannot file for withdrawal in lower courts you have to file for withdrawal of section 498A in the Higher Court within your jurisdiction. You have to apply in the Hight court of your jurisdiction for the withdrawal of the case. High court have the power to quash the case of section 498A. You can withdraw the section 498A case as it is a compoundable offence. For withdrawal you have to file a withdrawal petition application in the court where the complaint has been filed stating you do not want to pursue this case and the reasons for the same.
Since the offence under Section 498a is a criminal offence, so for withdrawing the same you will need to file an application of withdrawal of case to the High Court of jurisdiction. Please mention that this is an application for the High Court to exercise its powers under Section 482 of CrPC and attach written affidavits from all members of your family stating that they have no objection to this withdrawal.
Then Section 498-A case will be quashed. You can also document the settlement that has been agreed between you and your husband and then file a Quash petition in HC and the case would be quashed.
Reference: Section 498A of Indian Penal Code
Section 482 of Criminal Procedural Code