Pvt School Notice Period/Annual Vacation (not counted) - school has already held my original certificate as a bond

Hi All, Just want to opinion on the below:
I am working in a Pvt School in Bangalore. As per their contract, the notice period is 3 months. I have submitted my resignation on 19th Feb and Ideally, they should relieve me on 19th May. But, now from 19th April, the school vacation starts for a month & they are telling that if you want to relieve on 19th April, you should pay 3 months salary, else you can come back from Vacation and serve the notice period for another 3 months. This school has already held my original certificate as a bond. Also, last one year they have paid only 70% of the salary. Let me know your thoughts on what I should do in this situation? I am a little confused and worried. Thanks for your response.

it is always stupid to give your original certificate to the employer.
Their contention is wrong but now you are at their mercy.
One option for you is to walk off, file a police complain and also complain to the education department.
The other option is to get duplicate certificates from the concerned authorities
If you have DigiLocker, and your certificates appear on it, then they are adequate proof that you have qualified and the originals do not matter any more
However, you will still need to explain this to your new employers.