Employer refuses to pay overtime despite agreements. What should I do?

I work for an IT company in Bengaluru and have an agreement in my employment contract for overtime pay. Recently, despite logging over 20 hours of overtime in the last two months, my employer is denying any extra payment, citing budget cuts. I've tried discussing this with HR, but they are ignoring my emails. I'm feeling cheated and don't know how to proceed legally to claim my rightful dues. Am I entitled to overtime pay as per Indian labor laws?