Volercars - Refund not received

I was given the car with less than *-litre diesel (distance to empty showed as * on the dashboard). I returned the car with about ** litres diesel in the tank (distance to empty ~***km). I was promised a refund within **-** working days for extra fuel that I returned. First, they called me and said refund was approved for around *L fuel, because they considered empty tank as *L and what I returned was **L according to them. All this is in spite of them having the correct value of 'distance to empty' written on the trip completion sheet that was handed over to them. Secondly, It's been over a month since all this, and other than promising me a refund 'soon', I have not gotten a single rupee from them so far. I have spoken to customer care *-* times, and three times they said they would arrange a callback from a supervisor which never happened. They are basically getting away with stealing my money in broad daylight.