Byjus learning app - Cancelation of learning app

I purchased the Byjus Premium Product (learning app) for my son studying in the *th standard. I purchased it for Rs.*****. But he is not able to follow the app and I requested for cancelation of the App. But they are saying that it can't be canceled. Even if your son is not able to study you should make the full payment.
In the agreement, it is mentioned that cancelation should be done within ** days of purchase. When the executive came to our house for a demo but he didn't mention anything about the ** days. And he was in a hurry to get the agreement signed because the time he came was evening *.** and after the demo class the time was almost *. But in the agreement, it is also mentioned that the company will issue refunds for those cases which are eligible for refunds. I am not asking them to refund the amount I already paid. I am asking them to discontinue and cancel the EMI because my son can't follow that.
I asked the Byjus Mentor you give their Manager's number so that I can speak to them. But they are not ready to give that also.
Please do the needful.