Employer terminated me without notice after 5 years of service?

I have been working in a software company in Bengaluru for 5 years. Suddenly, my employer terminated me without any prior notice or reason. They haven't given me a termination letter and are refusing to pay my pending dues and gratuity. I’m worried about how to proceed. Is this termination legal in Karnataka? Can I challenge this in the labour court? I urgently need advice on what steps to take next.