Salary un-paid

I worked with a company (So called A), they placed me to work with (Company B) on contractual basis. On 31st March 2015, my contract got ended at Company B (Note: I never knew when my contract is getting ended because this information was shared only between Company A and B). On 1st April 2015, I couldn't attend Company B for work and I informed same to my HR / Relationship Manager in Company A. They informed me to wait till there further communication about contract extension or a project assignment. And they informed me that there will not be any issues with salary payment and they confirmed me that I will get my salary as usual. But due to contract conversion to permanent employment at Company B, I got into Company B and became a permanent employer. And resigned my job at Company A on 15th May 2015. As per offer letter and company commitment, I have to get my salary from 1st April 2015 to 15th May 2015 which is still un-paid to me. My financial situation is worse and I need the amount, but Company A is denying the payment. Please provide me further steps and advise. My Salary Per Month (Rs. 100000 - Rupees One Lakh)