Wrong vat purchases posted by someone in our account

Hi All

Our previous CA has posted wrong purchases in VAT for FY 2016-17 and 1st Qtr. 2017-18. Done as a revenge...... Our current CA was filing our VAT returns manually.... Now, Department is asking for Due Sales Tax on the Purchases never done. Moreover, all the purchases were filed as done from unregistered dealers.... So no whereabouts also.... Kindly suggest what to do in this matter ..... Plzzzzzzz help !!