Loss of pension documents

I would like to draw the attention of the postal department, Dhaka for investigation into the incidents of repeated loss of my pension documents in the postal department over last couple of years.
I) United Nations Joint Staff Pension (UNJSPF), New York, USA sent my certificate of entitlement for pension in October 2013 which was not delivered by Goran, Khilgoan Post Office to my address;
2) UNJSPF, New York, USA sent again a second delivery in January 2014, but Goran, Khilgoan Post Office did not deliver the same to my address again;
3) UNJSPF, New York, USA made a third delivery in October 2014, which was not delivered to my address in the same manner;
4) UNJSPF, New York, USA made the 4th delivery in January 2015 which had the same fate and was never delivered to my address.
I contacted the Post Master and the Post Man of Khilgaon/ Goran Post Office repeatedly, but still could not get the document in hand. Over and above, they did not pay any attention to my problem and remained totally indifferent about it.
The above deliveries are usual steps taken by UNJSPF, New York, USA or Geneva Office and accordingly the documents were dispatched to my address.
Other retired colleagues of mine living in and around Dhaka confirmed receipt of the similar documents through their post offices.
I shall be grateful if the postal department constitutes a committee to investigate into the matter and help me locate the documents and redress my difficulties.

Md. Joynal A. Bhuiyan
289/1 East Goran, Modina Masjid
Road No.9, P.O. Goran, Dhaka-1219