Incorrect billing - Cheating customers

I've had the worst internet broadband connection (Tata indicom) for nearly 2 years. They have the most awful customer care. Every month i have connectivity problems, and when i contact the customer care, they promise to resolve it in 24 hrs but they more than 3 days to resolve and they dont call back to confirm if the connection is fine after rectification. They have a stupid night unlimited scheme ( 9pm to 9am free) for which we pay an additional Rs. 299 every month. Last month, on 3 days, I started using the internet at 9 pm and used upto the next morning 6am. For that they charged me Rs. 200 on each day and at the end of three days I was charged Rs.600 and my connection got terminated because of account nil balance. I contacted the customer care for more than 10 times and no one was able to reply properly to my query and after 20 days they came back to me and said I had started using the connection at 8.59 pm and so I've been charged for the entire night usage. They did not refund my money and closed my complaint. They are so happy to let go of a customer. After all they cheated me and earned Rs.600 last month. If they do like this to every customer, imagine !!!