MoneyTap — GST on EMI

Moneytap claims that if their Banking partner charges GST on EMI, they reverse the GST charges to the account of customers. But now when I've been charged GST and post raising the issue they are claiming that the banking partner has changed the policy (I've already paid 10 EMIs out of 8) and I'll be charged GST and Moneytap will not reverse the same. They are clearly cheating the customers. Please address the complaint on priority.