composition/regular return in GST 2017 18 - Goods and Services Tax - GST

During the period july 2017 to march 2018 a dealer paid its tax liability through GSTR 3B as regular tax payer. However from date-14/08/2017 to date-28/11/2017 tax payer opted composition u/s 10 but flied its GSTR 3B as a regular tax payer. now a department issued intimation u/s 61 for excess Av ailment of Input tax credit in GSTR 3B compared to reflected in GSTR 2A . Difference relates to the period sep to nov because 2A has not available on GSTIN Portal. my query is Input tax credit claimed in GSTR 3B of Sep to Nov can be allowed or not or the department reject GSTR 3B on the ground that the tax payer has opted for composition.