Is it legal for my employer to keep my original documents after resignation?

I recently resigned from my job in Bengaluru, and my employer is refusing to return my original educational certificates. They say it's company policy until I serve a three-month notice period, but I only served one month. This is affecting my ability to join a new job as they require these documents. It's been two weeks and I'm feeling really stressed out. What are my rights in this situation and how can I get my documents back?