Urban Company - Why cancellation charge of Rs 100 was deducted

I booked for Split AC servicing and paid on line Rs. ***. Urban Co. Sent two people and they inspected the AC and said Gas has to be filled up and the cost of Gas is Rs. **** and the filling charges Rs ****. It is shocking to hear the cost and they said that this is UC rate. We requested for reduction as the Gas cost in the market is Rs. *** to Rs ***. We requested them to do the servicing without filling Gas but they did not agree. Hence we had cancelled the Booking. This is not our fault and hence the Rs. *** booking cancellation charge should be refunded immediately. This is unfair and unethical. This is what the truth is. UC should be told that they have no right to take booking charges in advance and later not refunding in full in such cases