Ola Cabs - Ola charged me double

I have booked a cab for my father who is a senior citizen through Ola postpaid. When the trip got over the driver asked for a higher amount (***) from my father at first and then charged his *** in cash despite me paying for it beforehand. Generally, if the amount is already paid it displays * in the driver's app but still, he charged *** in cash from my father.
The driver simply duped my father and is now denying that he took cash from my father.
You can even ask the fellow rider who was then present in the car. When we complained about the incident to OLA they simply said that it's our fault that we paid cash and since the driver is defying no refunds will be made. What sort of cab service is this where the driver takes advantage of senior citizen and dupes them.
Driver 's name was SK Wasim and his phone number was: ***** *****.
I want justice because if this is happening to my father this can happen to anyone.