Increment related

HI MY NAME IS KSHITIJ. I AM WORKING IN A BPO ON TEMPORARY BASIS. PAYROLL IS PROVIDING BY THIRD PARTY. I COMPLETED ONE YEAR IN THIS COMPANY BUT WHEN I SPOKE WITH THEM FOR INCREMENT THEY ARE DENYING FOR IT AND AFTER 2 YEAR THEY CHANGE THE VENDOR AND HIRE ANOTHER VENDOR (THIRD PARTY) IS IT LEGAL ?? ON THE OTHER HAND PEOPLE THOSE WHO ARE PERMANENT GETTING INCREMENT EVERY YEAR BUT THEY DO MORE WORK COMPARE WITH US. THE LAST THING WHICH I WANT TO ASK IS how long can employ a temporary employee in india ??