I am unable to find the first letter I received along-with approval of Tier 1 (General) in Dec-2009. All I have is the VISA stamp on the passport. When I applied for extension last time in 2013, I do not remember what I filled as reference number last time, so my big mistake of not keeping the copy of the filled application form

Can you kindly suggest other ways of finding this reference number? Also I am going first time for personal appointment so want to know if this will help me keeping it open and asking UKBA there.
Thanks in advance!