Experience Letter/Relieving letter not provided after resignation

Please assist, I was working with one of the top IT MNC and I resigned the Organization and fulfilled all the requirements necessary for the resignation process- served Notice Period, received the resignation acceptance letter and then I relocated to another state right after receiving the resignation acceptance letter on the same week. Date of Joining : 06 Dec 2010 , Resignation Date : 02 Jul 2011, Last Working Date : 30 Aug 2011 Received the resignation acceptnace letter from HR Dept. on 2nd September 2011. Received full and final settlement amount on my Bank account on 12/11/2011. FnF Settlement letters and Experience letter not received and after relocating I joined another MNC providing the resignation acceptance letter and continued working there. Now that I am about to join another IT Giant MNC and this new MNC is asking me to provide the Previouse Experience letters which I have not received so far, I started contacting the HR of the previous MNC and he directed me to another dept for checking it as he told that he is not the right person to apporach for my issue, I have sent couple of emails on the email address provided to me for obtaining my letters and I have not received any respond so far. I am lost and I need to join this new MNC soon and need to provide the Experience letter of this MNC. Please help me on How to obtain my Experience letter so that I can join this new IT MNC with no trouble. I have spoken to HR of this new IT MNC and HR insisted me to provide the Experience letter or else my verification will be invalid for the position. I understand that its been 5 years and as I was working ,I have never realized to obtain the letters and I almost forgot to collect or follow up on it. As per the policy I was supposed to received the letters in my new mailing address, I also updated the information of my new mailing address to the HR dept using the email communication and have all this emails communication with me. Please guide me on how to obtain my Experience letter as I need it on priority.