Byjus - Byjus app cancellation

Last Sep ****, I got a call from Byjus by asking the details of my children and their educational background. Byjus representative said their company offering some assistance free trial basis for the children. Later in the evening, he came to my house and he gave tab to my child who is studying in *th standard. He said that is for free for ** days trial. Later, if it is interesting, can continue till **th standard. He collected from me a cheque for Rs. *****. Next * weeks my kid used the same also she was getting calls from byjus app team every week. During her *nd term exam preparation time, she said some of the chapters not finding in the tab also some different chapters find in it. I made a complaint to the byjus team. Got some frequent calls in the next few days but they couldn't give a proper answer to why she is not finding the chapters as per the textbook. Earlier their promise was it will be same as textbook. Slowly they stopped calls also my kids stopped working in it. I made a call to the executive and cancelled the package. Next *-* months there was no reply from them. Later they made a call after *-* months that they going to debit the payment from the bank. I said why should we pay for the cancelled item also the tab which they are provided with my child not using too. As it is not helpful for the child please collect and refund the payment. Again there was no reply for a few days. But next month they collected Rs. **** from my back through ECS. I put a request to the bank for the stop payment with proof the mail which is sent to Byjus. I have sent several emails but they didn't respond to any emails. Instead, they started threatening me through phone calls. When I asked why should I pay for a product which is not using by my child they said whether using or not they need the payment as it is there in the contract. If I need to cancel it should be within ** days. In those days there were no issues my child was using it. Later once she finds which is not matching with her subject we made complaints but they couldn't correct the same. Now daily I am getting threatening calls from them in my office hours. Requesting your help on the same. Attaching the letter sent to the bank also to Byjus.