Cancellation of invoice in gst

Dear Sir,

we are a consulting agency. In august our one candidate join one of our client but after a few days he drop the job due to some reason we got to know that fact after 2 months. We have raised the invoice in august to the client but we have not received any payment from client and client is no accepting the invoice because he is not received any service from us ...we have already paid gst on that invoice at the time of GSTR-3B  ......now what is the treatment of that invoice in GSTR-1......can we cancel that invoice ....

Thanks in advance