Byju Classes - Byjus subcription cancellation

We have opted for Byjus online classes for my child for classes * to ** th, they assured that we can go for cancellation within ** days of period after activation if we dont like the classes, and they have taken the complete payment of rs *****, since we dint like classes and becoming hectic for my child, even he is suffering of sight issues we have asked for cancellation.
Instead of cancellation now these people are torturing us by calling frequently and asking to keep up the subscription.