GST invoice mistake

Both companies belong to the same group but different gst number samesame  signatory.

Last minute hurry isued 1 cheque now accountant requires 2 seperate invoices which insurane company refusez to give

Insurance company says since I issued 1 cheque they have already filed gst and now even though I have 2 gst numbers since I gave only 1 cheque it cannot be reversed.

I need a detailed solution please

Sir  I believe in case of group medical cover for employees of a company GST credit cannot be claimed. 

Please correct me if I am wrong/right

My important question here is can the insurance company issue 2 invoices if I have given only one cheque especially now that they have accounted for the same.