TDS on Advance amount received

one of my client is a works contractor and he has raised a bills For RS.1,80,00,000 and uploaded GSTR 1 for the same. But he has received RS.50 lakh as advance between Dec 17 to March 18 and he has not collected any GST for the same as per the notification w.e.f. 13/10/17. But the company has deducted IT for The total amount of RS. 2.3 crore. Now which is the turnover for my Income tax and what about the difference between IT and GST turnover. Can anybody explain me regarding this.