Central Board Of Secondary Education [CBSE] — School forcing us to join unknown application (Unacadmy) without giving any reason

Address:

Saint George Sr Sec school, berasia road opp. To bhel bhopal

My younger sister is studing in class 8 and today in the school group officials send a link and instruct to fill it we did as they said, and then it automatically joined us in a group where there was no school officials and just 2 people as admin and they are from unacadmy (the online Institute)
And now school is forcing us to login and give our details to it and now they are threatening us that if we didn't do so they are going to give names of students to principle and they will take action, I need help