Salary Hold, Relieving letter and experience letter hold

Respected Sirs, I have been in this company for almost 5 years. Im currently in a mid senior level. When i joined this company, in my offer letter there is nowhere mentioning about the NDA (Non Disclosure Agreement). Throughout my 5 Years, No complaints has been there and i have been the best performer in this company. I have handled so many big clients also as well. I served 2 months notice period completely and got the approval from my hr and my manager as well. Right now because of fear. During the last day, they are asking me to sign the nda. The NDA states that, for 2 years i have no rights to join any competitors (im working for a digital media company) and also even i have no rights to consult or do nothing if it was a Ex- Client. Literally, I have no rights to work on this industry for 2 years. 1. Is this legal? 2. Can i file a case against them? 3. If i filed a case against them, what are the possibilities to win this case. Note: Im having a kid. This particular issue has caused me so much trouble in my personal life. I worked for them literally with my blood and sweat. Kindly help me sirs