Cancel GST wef 01-07-2018 Refund of wrongly paid GST in Sept 19

1. My Clients have cancelled GST No. wef 01/07/2018 All return have been filed within due date.

2. In last month 18 Sept 2019  wrongly   GST Rs.6600/- paid to Cancel GST No.

3. For last Four days I am trying to apply for Refund of wrongly paid GST amount but online accepting bar are not highliting.

4. Let me know the procedure how can i claim wrongly paid GST    to cancel GST no.

5. Thanks in Advance.   Awaiting for valuable reply.