Gst invoice

I have received a Transfer Adjustment bill from the employee who was transferred from Port Blair to Vellore.  The individual has shifted from Port Blair to Kolkatta by ship and from there by Road to Vellore.   He got the bill from Port Blair for the Road transport and he has raised the GST invoice under UGST.  How come the GST Invoice can be raised from Port Blair whereas the Lorry was booked from Kolkatta to Vellore and it should have been IGST instead of UGST.  when I questioned the same, he got  a new GST Invoice from the same company at Port Blair with IGST.  I apprehend both the bills are not genuine and it will be shown to the GST authorities.  Though we didn't claim any input tax, and it is only a reimbursmeent to the employee,  the employee had submitted a fabricated bill and it is not the origianl one.  If i ask for the GST payment made by the company(as the bill was raised during August 2018) during September,2018.  But my colleagues says that even if get the GST returns of that company, i cannot prove that it is bogus.  Kindly advice.