Sahaa Coaching Centre - Poor response and denial of refund

I have joined German language class at Sahaa academy townhall Coimbatore India with payment of Rs.*****. After joining the class it is found that the teacher is not certified postponed classes and misses classes. They have not given any materials tools for study.
Due to their poor response, I have asked them to refund the money. But they denied that the payment receipt has a clause staying that the payment cannot be refunded on any occasion.
This clause they haven't told us before making the payment. After making payment only I come to know.