Employer refusing to pay pending salary after resignation, what can I do?

I resigned from my job at a private company in Mumbai last month and served the full notice period. However, my employer is refusing to pay my last month's salary, citing some vague performance issues. I fulfilled all my duties during my notice period and have emails to prove it. It's been over three weeks since my last day, and I'm really worried about how to recover my pending dues. What are my legal options to address this issue in Mumbai?