No overtime pay nor vacation leaves

I am working at a 5yr old software company with 100 employees in Chennai and couple of other locations in India. My employer is not offering the overtime pay. The general shift consists of 10hrs a day, but being forced to work for 12 - 15 hrs a day without any overtime pay. Same goes with the vacation leaves, there are no vacation leaves being offered. If asked about it the response was "No overtime pay and vacation leaves in the company policy". i am working there since past 3yrs. if anyone wants to leave the company they are being told that "we will not provide experience letter if you leave, you need to work for another 3 to 4 months even though the notice period is 2 months".. If voiced strongly they were told "we will put remarks on your profile or file a case etc.,". No official hike or promotion letters being provided annually even though the titles and increments are given. People who got terminated did not get any pay for notice period nor promotion letters. Is there anything we could do to make a safe exit.