Need Help in GST for Company Car Lease

Hi All

I really need help as I have had to
resign due to some unforseen circumstances and have a company car lease under my name from HCL for an Alto.I took this lease in April 2017 when GST was not in effect.Now i know i have to buy back the car from the company but now they have put a GST of 18.85% on the car's IDV. When i did not pay GST then so can my organization charge me GST for buying back the car? I tried looking for articles about this but no luck so far. Anyone's help will really be appreciated.