Gst on Refund of Bank Guarantee Commissioner

Co. X is engaged in infrastructure services on contractual basis for the Government. Co.X provide Bank Guarantees to Govt., Creditors etc. For Eg:
BG amount - 100000
Bg issue date - 01.04.2020
bg Claim period - 01.04.2022
bg validity - 01.04.2021
Bg commission charged - 4800+864 (basic amt +18%gst)
Now if Bg gets cancelled on 30.04.2020 and we take refund of Bg commission should the bank reverse the Gst or are we suppose to collect gst on Refund of Bg commission or we won't do any of it?