Arrears amount not being paid by the employer...

Hi, I'm Yogesh working as Design engineer at a company named "Harita Techserv Limited" from past 4.5 years. Basically i am sent t work onsite at client location and now (After 4.5years) client has decided to absorb me as direct employee. Since this year starting i was about to complete my 6 years of overall experience, my employer asked the client to increase the amount in my name so that they can offer me hike for this year as their margin of profit was quite low in my name. Client may have thought on the same or may be some other reasons, they agreed to give me direct offer. Now situation is: 1. Harita kept my appraisal on hold (while others received their letters by April end which was mentioned as effective from 1st April). 2. Gave me the offer in May saying as ""effective from May1st" which is not valid. And i have replied them for that concern. But no replies from company. 3. Now salary hike is given effective from May but not for April (Atleast as arrears) 4. I have put mails and calls, and hearing that its not possible to give April arrears. Please let me now as legally if i go against Harita, what are my chances.