School not giving out the TC

Hello, I am James . Sir, I would like to know if a school can make the students to sign a bond stating that they would continue to study in their school after the Board exam. The School is holding on to the class 10 certificates saying they have a bond that was signed by the students . They are not giving out the certificates, on this account. In fact, the signature was taken when they conducted a pre-board exam coaching for a month. We had no idea it was a bond. But when we went to claim the Board certificates, they showed us this writings in the previous page of a register book, stating that the students below have promised to continue studing in this particular school. Sir , i would like to know if its legal to make the students sign a bond . Isn't it illegal to make a 15 year old to sign a bond by the school ?? We thought we were signing up for the coaching but turns out it was a bond . The bond was never shown to us. They just asked us to sign in amongst the rows of of signature of the students. Sir please help us. We have no idea what to do. Its been about a week and they are still not giving out the certificates.