Zoomcar India Pvt Ltd - Zoom car not refunding the fuel expense

I am from Bangalore and booked zoom car (with fuel option) in jaipur from ** December **** to ** December **** to travel around Rajasthan for sightseeing. Many petrol pumps didn't share the fuel bill while filling fuel in the car. Since there is no helpline number in the zoom car app to call and ask, I always paid with credit card and thought I can provide sales receipt. I returned the car in Udaipur as per the booking on time and even the zoom car executive who collected the car informed me that sales receipt is acceptable and helped me in uploading it into the app for refund. After some days I received from Zoom car, a final payment bill for Rs **** for extra kms traveled which is genuine since I traveled extra kms but it didn't mention anything about the fuel refund. On sending email to zoom car customer care, they mentioned since the sales receipt didn't have any fuel information and hence they can't refund the money to which I replied that the petrol pumps didn't share any bill with me even when I asked. I told them there is no way I could have traveled ****kms over * days without any fuel being filled into the vehicle and since I already booked for a car with fuel, it is there obligation to refund me the fuel amount or convert my booking into a without fuel one. They are not agreeing to my claim and one customer care executive even threatened me with legal action if I don't pay the Rs ****, which I told I won't pay if you guys don't hold your end of the bargain. The amount I claimed is Rs ****(which is totally reasonable for traveling **** kms) for which I had provided sales receipt. Now my question is "If there is irrefutable evidence to suggest that the customer has filled in fuel (**** kms cannot be traveled without filling in fuel), and provides sales receipt (since the bills were not shared by the petrol pumps) and has paid for a zoom car with fuel, why are they still not refunding the fuel amount? "