GST Rate on buyback of company leased card

I had bought CAR on company lease policy and lease was from TATA capital.  After completion of lease the CAR has to be bought back by me by paying 15% of residual value.  The original GST charged during purchase of car was 28% and CESS of 17%.  When the car is bought back by TATA has charged the GST of same rate of 28% and 17 CESS. The HSN mentioned is 87030017.  I want to confirm if the rate of GST and CESS is correctly charged or it should be be 18% since this is like buy back of second hand car. I am attaching the Invoice copy for your ref.  Your help is appreciated.