Casual gst registration

My casual registration got inactive as 90 days has been completed, now the status of GSTIN inactive. One bill which was uploaded in GSTR-1 of previous period ,when registration was active, got amended due to which there is need to amend the bill and pay the additional tax liability with interest. As the GSTIN is inactive, i am not able to file GSTR-3B and GSTR-1, also there is no option for filing GST REG-11 (extension of casual registration). 

Please clarify, how to resolve the issue?