Delaying or denying Full and Final settlement and service letter

Hi, I joined Teksystems as a contractor employee on Feb 2014 and client was Dell international services. In the agreement job termination notice period was 15 days from both side. On July 4th 2014 I had received termination letter from Teksystems which does not mentioned any valid reason for termination and the mail stated that “you will be relieved from our services effective 17th July 2014”. I believe last working day should be 4+15 = 19th July as per agreement. When I reached Dell office very next day, I have been asked to surrender all Dell belongings including access/id card and laptop etc.. and not allowed to enter office except reception area. I contacted my Dell manager for reason why security is asking to submit all my Dell belongings, he informed me that the contract has terminated on 4th July. Later after one month I joined in Dell as direct payroll. From that day I am trying to get my full and final (arears for 1st to 17th/19th July) and service letter. I have send several mails to Teksystems for this. Till now I haven’t received positive reply from them. Please advise me on this. Am I eligible for arears from Teksystems for above mentioned dates? What I can do for getting my service letter? I am facing difficulties to switch my job as every employer is asking for service letter from previous company. Am I eligible for any compensation for this? Sincerely , Abilash T.A