Mahindra Electric Mobility Limited — Collection of GST on battery for car purchased in DEC 2015

Hi,
i had purchased an Electric Car E20 in DEC 2015 and as per available scheme had opted for payment of battery charges in installments through ECCS for INR 2999 for 5 years, now even after completion of the 5 years term, did not receive NOC and found the ECCS is debited from my account, when requested was sent to company to issue NOC, got mail reply stating i have to pay GST for the same and outstanding amount is 56218/- INR. The ECCS deduction started from FEB 2016 and payment was done till April 2021, when asked why i should pay GST for something which was purchased before GST was introduced,

Mahindra and Mahindra seems to be fraud company and no idea how much they have collected from customers till now.