Return not filed

No option for take input tax credit on purchase because availing old invoice with GST is not possible because it affect the counter party filled GST returns. Due to no purchase Showing Sales even as b2c is waste. So start proper filing from sep 2018 onwards.

If you have not file GST3B, GSTR1 Return from OCT 2017 to September 2018 then you have to file without any Penalty upto 31st March 2019 as per government notification.

Government Notification: The finance ministry has finally waived the late fees for taxpayers who were unable to file GSTR-1, GSTR 3B or GSTR-4 for the period July 2017 to September 2018 by the due date but furnished the same between 22 December to 31 March 2019.

You cannot claim without filing your previous return.

After filing your previous return you can claim ITC.

Hope it helps you.