Employer terminated me without notice after 5 years of service. What can I do?

I've been working at a tech company in Bangalore for over 5 years. Suddenly, they terminated me without any notice or severance pay. I feel blindsided and unsure about my rights here. I was told it was due to 'company restructuring', but I suspect it's because I raised concerns about unpaid overtime. How can I approach this legally? Can I file a case for unfair dismissal in the Karnataka Labor Court?