Cognizant Technology Solutions — Asset clearance is pending

My last working day in Cognizant was 15th April but I have not still received my relieving letter and experience letter. when I open onecognizantexternal portal i see my Asset/NSS approval is still showing pending. I have already returned my asset(Laptop) through the Vendor and it is also received at Cognizant office but still my NSS approval is pending. When I mail to NSS approval team they don't reply. I mail them daily but i don't receive any reply.
I don't understand what I do as the relieving letter is very important document.
It's been more than 2 months but still I don't receive any communication regarding my approval from them.