Byju Classes - Stopping of mandate for not continuing byju package

We had taken a demo class from byju and deposited Rs. ****/- as token money for which trial classes were offered. We tried to contact the contact person for closure of the same as the kid was not able to pursue the same with school classes. But the byju person did not take a call and now they say that the period of trial is over and we shall have to make the full payment for which we have signed the mandate. we have not used the service and as such we should not be forced to pay for the same.we are asking to revoke the mandate that we have given.