Employer refusing to pay me for extra hours worked over the past 3 months?

I work in a software company in Bengaluru and have regularly been asked to work overtime for the last 3 months, often logging an additional 10-15 hours weekly. However, my employer has not compensated me for these extra hours, citing budget constraints. I am feeling frustrated as I rely on this additional income to manage my expenses. When I approached my HR, they said it will be adjusted in the future, but there is no clarity on when. What are my rights in this situation, and how can I ensure I get paid for my overtime?