Ola Cab Kolkata - Overcharging after ride completed without alert

I booked Ola Rental cab(CRN no.**********) on **/*/** at **.**am for * hours **km for Rs.*** plus tax, reading every single terms and conditions a few times, just to be sure that I wouldn't have to pay a single rupee extra. While booking ola app shows package RS.*** plus tax *hours **kms(exceeding charges rs.*/km and rs.*.*/min) cannot be changed after booking. That was our contract. Rode the car in city for *hr** minute and **.*km. At the end of the ride the bill charged for the ride was RS.***. I was charged extra *** plus tax shockingly as Price Increase, which was never alerted to me before/during the booking and was never even mentioned in the terms and conditions (where it was/is clearly stated that only exceeding the limit of km/hr extra charge would cause extra bill and there was not a single mention of Price Increase at the end of the ride as a surprise or in general). I have all the screen shots of ride booking and tnc. I know what are the loopholes ola and uber uses. Uber Rental cab shows various charges at any point of time but Ola Rental shows same price anytime. I didn't cross any limit and neither I was alerted for any extra charges that can be levied so clearly what ola did was unethical and improper business conduct. I contacted ola customer service on **nd June and a few times after but they didn't refund or give any proper explanation of why it was charged at the end of the ride shockingly without any alert before ride booking or why it was never shown to me before ride booking. For that I demand the refund of RS.***(*** plus tax) and apology from Ola cab or I will take legal action on the ground of unethical fraudulent business conduct.