OLA - Ola cab not refunding my remaining coupon amount

I had * coupons of OLA cabs Rs**** each. I confirmed this will them first that if I take a ride of a lesser amount say Rs***. What happens to remaining Rs***. They confirmed to me over mail that another coupon of Rs*** will be generated and that will reflect in the app.
When I used the voucher for Rs*** ride, the remaining Rs*** was not generated. Upon sharing this with Ola Support, they deny to me now, telling me that I have not used any coupon.
I have proof of using the coupons in Ola invoice itself. But they are not accepting it.