Hi Pavan,
Not sure which SAP EWM version you are using, but now in 9.02 you can reverse the GR material document from ECC and then process in EWM to cancel the Inbound delivery.
Try to reverse your ad-hoc goods issue and once the stock available then try to cancel the original GR. I am not sure this will really work. but give a try.
Also, always make sure your integration model always active for the material to avoid this kind of situations in production environment. I hope you are checking in test environment.
Thanks,
Sandip