I purchased some material for my civil construction work , my supplier filled his GSTR 1 return in 12 July 2020 , Corona time , for the month of March 2020 and I claimed the input tax credit in March 2020 Gst 3b return only , now I got a call from Gst department for the differences, they want me to show the reconciliation  between Gst 2a and Gst 3b, What should I do now ?